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Dipmeter displacement processing technique In order to determine dips of subsurface formations more reliably, a dipmeter tool with three or more transducers, spaced circumferentially around the borehole wall, is used and the transducer outputs are correlated in a novel way to provide redundant indications of displacements between the depths at which respective transducers intercept a given layer. These redundant displacements are processed to single out at each given level only those displacement pairs which result in the most consistent dips over several mutually overlapping depth intervals called zones. Consistency is established in each zone without regard to a neighboring zone, to avoid any long range bias.
Primary Examiner: Atkinson; Charles E. Assistant Examiner: Jablon; Clark A. This is a continuation of application Ser. No. 537,998 filed Dec. 30, 1974 and now U.S. Pat. No. 4,348,748. What is claimed is: 1. A dipmeter well-logging method comprising: deriving a transducer response log for each of three or more transducer paths which extend along at least a selected interval of a borehole traversing subsurface earth formations and are circumferentially spaced from each other around the borehole wall; finding for each respective pair of said logs and at each of a succession of respective depth levels in said borehole interval, the depth displacement between a base correlation interval of one of the logs of a pair and a similar interval of the other at which the two intervals best fit each other, thereby typically deriving three or more such depth displacements per depth level, wherein the correlation interval for one depth level substantially overlaps that of the next; finding zones each comprising respective borehole depth levels the depth displacements at which for at least two pairs of logs are consistent with each other from one depth level to the next within selected criteria for consistency; using said three or more depth displacements per depth level to derive therefrom two or more possible dips per level, each dip having a respective dip azimuth and dip magnitude, and finding, for each zone, one or more respective clusters of said possible dips, each cluster comprising possible dips which are within a selected range of dip azimuth and dip magnitude; for each depth level in the borehole, retaining only the possible dip, in any, which is consistent within selected criteria with a cluster which is for the zone including said depth level and meets selected criteria for cluster quality; and producing a tangible representation of said retained dips. 2. A method as in claim 1 wherein the step of deriving said three or more logs comprises passing through the borehole a dipmeter tool having three or more transducers circumferentially spaced around the borehole wall and deriving therefrom said transducer response logs. 3. A method as in claim 1 including deriving a respective log for each of four or more transducer paths circumferentially spaced around the borehole wall, finding four or more depth displacements per typical depth level and using said depth displacements to typically derive five or more possible dips per depth level. 4. A method as in claim 1 including weighting each of said three or more possible dips per depth level on the basis of the quality of the fit between the log intervals leading to the pair of depth displacements defining the possible dip and on the basis of the closure error at the respective depth level, and wherein said weighting is a part of the selected criteria for cluster quality. 5. A method as in claim 1 including associating with each retained dip a grading based on the number of possible dips contributed by the same depth level to the cluster which includes the retained dip, and including said grading in said tangible representation. 6. A method as in claim 1 including pooling into a single vector-average dip the retained dips from adjacent depth levels which are mutually consistent with each other within selected criteria for dip azimuth range and dip magnitude range, and including so derived pooled dips, rather than the retained dips leading thereto, in said tangible representation, to thereby reduce duplication of the same retained dip over a succession of depth levels in case of the presence of the same dominant anomaly in overlapping correlation intervals. 7. A method as in claim 6 in which the step of producing said tangible representation comprises producing an arrowplot of pooled dips and of retained dips not used in said pooling, each arrowplot dip indicating both dip azimuth and dip magnitude, said arrowplot indicating the borehole depth level of each dip shown thereon. 8. A method as in claim 1 in which said tangible representation comprises an arrowplot in which an arrow represents a respective retained dip and indicates both dip azimuth and dip magnitude, said arrowplot indicating the borehole depth level of each dip shown thereon. 9. A method as in claim 1 in which each of said transducer response logs is a microresistivity log of said borehole. 10. A dipmeter well-logging method comprising: deriving logs for three or more transducer paths which are circumferentially spaced around the wall of at least a selected interval of a borehole traversing subsurface earth formations; matching portions of said logs by the use of the substantially overlapping correlation intervals to derive several possible dips for each of substantially all of the depth levels in said borehole interval and retaining only those dips which tend to repeat from one depth level to the next within selected depth zones, to thereby retain a single dip for each of substantially all depth levels in said borehole interval; and producing a tangible representation of the retained dips. 11. A method as in claim 10 in which the step of producing said tangible representation comprises producing a dipmeter arrowplot in which an arrow shows both the dip azimuth and dip magnitude of a respective retained dip and the arrowplot shows the borehole depth level of each dip shown therein. 12. A method as in claim 11 including pooling dips from adjacent, highly stable depth levels into a single vector-average dip and plotting in said arrowplot the pooled dips in place of the retained dips used in said pooling. 13. A method as in claim 10 including passing a logging tool having three or more transducers through said borehole to derive said logs. 14. A method as in claim 10 in which each of said logs is a microresistivity log taken along the respective transducer path. 15. A dipmeter well-logging system comprising: means for deriving a transducer response log for each of three or more transducer paths which extend along at least a selected interval of a borehole traversing subsurface earth formations and are circumferentially spaced from each other around the borehole wall; means for finding for each respective pair of said logs and at each of a succession of respective depth levels in said borehole interval, the depth displacement between a base correlation interval of one of the logs of a pair and a similar interval of the other at which the two intervals best fit each other, to thereby typically derive three or more such depth displacements per depth level, wherein the correlation interval for one depth level substantially overlaps that of the next, for using said three or more depth displacements per depth level to typically derive therefrom two or more possible dips per level, each dip having a respective dip azimuth and dip magnitude, for finding zones each comprising respective borehole depth levels the depth displacements at which are consistent with each other from one depth level to the next within selected criteria for consistency, and for finding, for each zone, one or more respective clusters of said possible dips, each cluster comprising possible dips which are within a selected range of dip azimuth and dip magnitude, and for retaining, for each depth level in the borehole, only the possible dip, if any, which is consistent within selected criteria with a cluster which is for the zone including said depth level and meets selected criteria for cluster quality; and means for producing a tangible representation of said retained dips. 16. A system as in claim 15 wherein the means for deriving said three or more logs comprises a dipmeter tool having three or more transducers circumferentially spaced around the borehole wall and means for passing the tool through the borehole. 17. A dipmeter well-logging system comprising: means for deriving logs for three or more transducer paths circumferentially spaced around the wall of at least a selected interval of a borehole traversing subsurface earth formations, for matching portions of said logs by the use of substantially overlapping correlation intervals to derive several possible dips for each of substantially all of the depth levels in said borehole interval and for retaining only those dips which tend to repeat from one depth level to the next within selected depth zones, to thereby retain a single dip for each of substantially all depth levels in said borehole interval; and means for producing a tangible representation of the retained dips. 18. A system as in claim 17 in which the means for deriving said logs includes a well logging tool having three or more circumferentially spaced transducers producing said respective logs and means for passing the tool through said borehole to derive said logs. BACKGROUND OF THE INVENTION This invention relates generally to techniques used in geophysical well logging, and more particularly to new techniques for automatically processing dipmeter signals or displacement measurements obtained between these signals to produce more accurate dip and azimuth representations of subsurface formations. A common method of measuring the dip angle and direction or azimuth of subsurface formations employs a dipmeter tool passed through a borehole drilled into the subsurface formations. This tool may apply any of numerous means to obtain geophysical signals representative of variations of a particular formation characteristic, such as its resistivity. One such tool is described in the paper: "The High Resolution Dipmeter Tool", by L. A. Allaud and J. Ringot, published in the May-June 1969 issue of The Log Analyst. Dip and azimuth measurements representing the inclination of a formation characteristic or feature may be determined from dipmeter signals containing information representing the intersection of such a feature at three or more radially spaced points on the borehole surface. The displacement between two points intersecting a common feature may be determined, under favorable circumstances, by correlating pairs of the dipmeter signals, each having a similar response to the common feature. Two displacements between three different points determine the position of a plane. The position of the plane is conveniently expressed by its dip .theta., an angle measured from a reference (usually horizontal) plane and its azimuth .PHI., an angle measured from a reference direction (usually true North). Typically, the dipmeter signals are recorded on computer compatible magnetic tape at the well site for later processing. The recorded signals are processed using any of several techniques. Manual, semi-automatic and fully automatic processing may be used with the automatic processing before performed with either analog or digital computers. When digital computers are used, a computer program is also required. A computer program to perform the digital processing operations is described in a paper, "Automatic Computation of Dipmeter Logs Digitally Recorded on Magnetic Tape" by J. H. Moran, et al and published in the July, 1962 issue of the Journal of Petroleum Technology. An additional computer program is described in the paper, "Computer Methods of Diplog Correlation" by L. G. Schoonover, et al, pages 31-38, published in the February 1973 issue of Society of Petroleum Engineers Journal. Further, programs to process digitally-taped dipmeter data may be obtained from digital computer manufactures, such as IBM. Results from digital processing are normally presented in tabular listings as dip and azimuth measurements versus borehole depth. When desired, the individual displacements found between the correlated curve pairs which led to the dip and azimuth values may be also presented. Further, most such programs will provide the ability to vary both the length of the correlation interval and the step used to move this interval between each correlation sequence. For the next sequence, the same correlation length is used, but the actual interval correlated is moved by one correlation step length. At each step or depth level, one sequence of displacements between various pairs of signal combinations may be obtained. A typical sequence includes at least two displacements but may include a round of up to six displacements in each sequence when four separate signals are employed, for example. When a round of more than two displacements in one sequence is obtained, the displacements may be combined into many more possibly different combinations, each combination corresponding to perhaps a different dip and azimuth measurement. Since only two related displacements are required, it is common practice to utilize only what appears to be the two best qualified displacements. All others are discarded without further consideration, thereby producing only one result per sequence. Further, little is retained as to the position of the sources or dipmeter pads corresponding to the utilized displacements. When large numbers of measurements result, as from recent high resolution dipmeter techniques, tabular listings are usually augmented by graphic presentations of dip and azimuth representations. The graphic displays vary with the interpretation objective, depending upon whether the purpose is for stratigraphic or structural studies. Accordingly, relationships between the corresponding dip and azimuth measurements and their continuity with depth are considered in different manners. For stratigraphic purposes, trends of adjacent dip measurements with depth are usually used to classify the measurements. For example, measurements representing a trend of rapidly increasing dip with depth will be considered separately from measurements representing a trend of rapidly decreasing dip with depth. In the stratigraphic analysis, it is important that the azimuth of these dips must remain substantially constant and thereby represent the general direction of sediment transport or perhaps the probable direction of down dip thickening. Also, dipmeter results are combined in a given analysis from intervals corresponding to a given depositional or stratigraphic unit. Graphic displays used for stratigraphic analysis often ignore the actual depths once the above dip versus depth trend for a given azimuth range qualifies a group of measurements. Further, since in many cases the actual dip angle is not important and only the dip azimuth is significant, the dip angle may be completely ignored in the graphic display. Such displays are designed to statistically determine the azimuth corresponding to a primary and perhaps a secondary direction of transport or deposition. Graphic displays used in stratigraphic analysis are typically the azimuth frequency plot (no dip or depth representation) and the Schmidt net and the Stereonet (azimuth versus dip but still no depth representation). These nets and several variations thereof have known statistical characteristics in that they may enhance either low or high dip measurement point groupings. Note that in their use, the dip and azimuth value for each measurement is combined and represented by a point in these nets. A description of some of these displays and their application is given in the paper "Stratigraphic Applications of Dipmeter Data in Mid-Continent" by R. L. Campbell, Jr., published September 1968 in the American Association of Petroleum Geologists Bulletin. Stratigraphic and structural analyses distinguish themselves in the type of information needed. In stratigraphic analysis, the dipmeter signals hopefully represent bedding planes within the boundaries of a given geological unit. These bedding planes have little, if any, regional extent. In structural analysis, a deliberate attempt may be made to mask out such sedimentary features in favor of enhancing the boundaries of the individual strata. Short lengths (1 to 2 or 3 feet) of dipmeter signals are correlated to obtain stratigraphic information while long lengths (10 to 20 or 30 feet) of signals are often correlated to obtain structural information. While use of long correlation lengths to obtain structural dip has been standard practice for some time, there are certain disadvantages associated with this practice. One is that the use of long correlation lengths masks dip patterns needed for stratigraphic analysis, thus additional computations must be made using a short length to obtain stratigraphic information. Another is that most long correlation length techniques may be influenced by frequently occurring stratigraphic features having a common dip and direction, even though each such feature is less pronounced then the structural feature. Thus, the use of long correlation lengths does not assure obtaining accurate structural dip information. Yet another disadvantage is that current correlation techniques tend to ignore possibly objectionable effects of rotation of the dipmeter tool within the long correlation interval. The preferred approach is to obtain the detailed information available only from short correlation intervals and then apply previously mentioned trend analysis to separate the stratigraphic and structural dips. However, as the correlation interval is shortened, the probability of obtaining a completely erroneous displacement increases substantially. The wrong peak on the correlation function produced in the correlation process may be used to determine the displacement. Such invalid displacements may be combined with valid displacements and produce an erroneous dip which add scatter and confuse valid trends or when systematically erroneous, may even appear as false trends. As a compromise, longer correlation intervals than are actually desired are employed to artificially reduce this scatter to an acceptable level so that any valid trend which may be present might be found. It is therefore an object of this invention to provide a technique to reduce the scatter in dip and azimuth measurements determined from short correlation intervals. One technique which is employed to reduce scatter and find dip and azimuth trends is to average long intervals of dip measurements obtained from much shorter intervals. Unfortunately, the valid trends present only as short intervals may be masked completely by such an averaging process. Further, the resolution and position of the correct peak obtained by correlating short intervals tends to vary considerably, consequently, the corresponding displacements lack accuracy. Certain combinations of such displacements may compound the variation and introduce unacceptable inaccuracies in the resulting dip and azimuth measurements. It is therefore an additional object of the present invention to provide a technique to improve the accuracy and reduce the scatter of dip and azimuth measurements without necessitating long interval averaging. Some of the averaging techniques include a preliminary process of sorting or discarding apparently stray dips before averaging to prevent their contributing to the average. This process adds both time delays and expense to a process which already produces too few dips for many purposes. Further, some of the apparent strays may actually be part of a valid trend which was unfortunately just sampled infrequently. Both the discarding and averaging processes suppress such valid dips. It is therefore a further object of the present invention to provide an automatic technique to improve the accuracy of dip and azimuth determinations without reducing the number of valid dips or discarding dips because they do not comply with some long interval trend. When such averaging techniques are employed, the intervals to be averaged are often chosen arbitrarily such as every 100 feet or the like. Yet such zoning or sample grouping is an important factor in most statistical analysis. In some techniques, independent geological information is examined (usually manually) to select specific zones to be averaged. This latter process requires considerable time as well as accurate coordination of the depths of the geological information and the dipmeter information. This depth coordination may be a problem in deviating holes where the dipmeter information might not correspond to true depths. It would therefore be advantageous to have the determination of zones be made from the dipmeter data itself. It is therefore a further object of the present invention to provide a technique for automatically zoning dipmeter information by analyzing the dipmeter information itself. As previously discussed, there are prior art techniques for statistically analyzing either the dip or azimuth information for long interval trends. These methods usually employ polar chart representations to classify the dip and/or azimuth measurements. In these plots, the dip varies with distance from either the center or the edge of the plots and the azimuth varies with the radial distribution from the center of the plot. However, when one considers the type of errors likely to take place in the correlation processes, particularly in deviated holes, it is desirable that any analysis not separate the dip from the azimuth values for the purposes of the analysis. The analysis should be able to detect any interrelationship between the dip and azimuth for the individual measurements. More particularly, the analysis should respect the fact that erroneous displacements can be concealed when expressed only as the resulting dip and azimuth measurements. It is therefore a further object of the present invention to provide a technique for analyzing displacements and combinations of displacements rather than computing and analyzing the resulting dip or azimuth measurements. Prior art methods of dip and azimuth analysis largely ignore the direction of the borehole when deviated. Yet this may be an important control on the distribution of the measurements. Due to the type of problems associated at times with the borehole tool operation, the position of the tool and the signal sources relative to the borehole deviation and direction should be considered in the analysis in case they are also a factor in the distribution of the measurements. Therefore, it is a still further object of the present invention to provide a system for analyzing displacements and combinations of displacements which considers the relative position of the borehole and the tool in determining the most valid displacements and combinations thereof. In accordance with these and other objects of the present invention, apparatus and methods are provided for automatically processing with a machine displacements obtained between geophysical signals derived from sources spaced at different positions to determine and producing recorded representations of the relative position of the features on said signals. In one form of the invention, displacements are obtained between similar features in overlapping intervals of geophysical signals which are derived from the spaced sources. Displacements between said signals which are found to be possibly corresponding are combined and these combinations classified as a function of the relative position of the sources. These classified combinations are analyzed to determine the position of the dominant class, from which the corresponding relative position of the signals may also be determined. When applied to geophysical signals derived in a borehole from separate dipmeter pads which are known to be spaced at different positions around the borehole, the position of the dominant class and corresponding relative position of the signals may be used to derive the dip and azimuth of a variation in a characteristic of a subsurface earth formation. In one feature of the invention the displacements are combined to generate for each combination a function representing a displacement relationship between any three related signals. These relationships are analyzed to determine the most valid combination of displacements. The analysis may be made in conjunction with other information such as the position of the signal sources in regard to the deviation of the borehole. In one analysis, the most valid combinations of displacements are those derived from signal sources which are substantially in contact with the borehole wall. In highly deviated holes, the above valid displacement combinations may be considered as the only possible corresponding displacements which may be combined and further analyzed to determine the dip and azimuth of a particular zone. In a still further feature of the invention, displacements are analyzed to determine the beginning and ending sequences of displacements corresponding to substantially stable zones of displacements. Displacements from sequences in such stable zones are then combined as possibly corresponding displacements for one analysis while displacements from sequences outside such zones are combined for another analysis. Since each corresponding pair of displacements in each sequence may be combined to determine a possible position of a formation feature, each displacement combination is retained for classification. Thus, many redundant possible combinations from each sequence, and from sequences in which the displacements were obtained from overlapping signal intervals, are classified. In the analysis of these classified combinations, some of these combinations may now be discarded, rather than, as in the prior art, discarding the redundant displacements at each sequence without further consideration. The retention of substantially all possible corresponding displacements and combinations thereof, even though they may appear to be of poor quality, for use in classification and analysis allows their contributions to accumulate with other combinations. Therefore, accumulations of weak but consistent displacements which are in face the correct ones, are not prematurely discarded. Further, apparently good quality but perhaps erroneous or inconsistent displacements will not be selected to compute the only dip and azimuth representations for the sequence. The techniques of the present invention recognize that what has been previously regarded as ambiguous or lesser quality information often contains important information. By retaining this information until contributed to the analysis, the invention utilizes information which was previously discarded for sometimes arbitrary reasons or, in some cases, never even computed. For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, the scope of the invention being pointed out in the appended claims. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 illustrates a method and apparatus for producing dipmeter signals, obtaining displacements between pairs of these signals and processing these displacements in accordance with one form of the invention. FIG. 2 illustrates how certain references relative to the borehole tool are measured. FIG. 3 shows how displacements obtained between similar characteristics on pairs of geophysical signals derived at spaced positions in a borehole are related to the plane of a formation feature intersecting the borehole. FIG. 4A illustrates in a view looking down the borehole one position a borehole tool may take in a deviated borehole. FIG. 4B illustrates the side view corresponding to FIG. 4A and shows how the measured diameter D.sub.1-3 may not correspond to the effective diameter De. FIG. 5A illustrates possibly corresponding displacements between two similar characteristics, A and A', on one signal and similar characteristics, B through D, on various other signals. FIG. 5B shows correlograms related to the possibly corresponding displacements illustrated in FIG. 5A. FIG. 6A illustrates additional possibly corresponding displacements between two similar characteristics present on the signal curves in the same correlation interval. FIGS. 6B through 6G illustrate, in simplified form, six correlograms and the corresponding displacements usually selected in correlating various pairs of the four curves illustrated in FIG. 6A. FIG. 7A illustrates the general characteristics of a correlogram in terms of correlation quality and displacement determination. FIGS. 7B and 7C illustrate how spurious peaks in a correlogram may cause temporary changes in what otherwise might be an essentially contiguous sequence of stable displacements. FIG. 7D illustrates how a valid change in the correlograms and displacements corresponding to a new formation dip may result in a break in the continuity of substantially stable displacements. FIG. 8A illustrates in simplified form how displacement distances Z determined between an electrode plane on the borehole tool and features on curves or signals derived at the electrodes may be treated algebraically to determine displacements. FIG. 8B illustrates in relation to diagonal pairs of electrodes the displacement distances depicted in FIG. 8A. FIG. 8C illustrates how these distances or displacements appear in a plane parallel to the borehole axis and passing through diagonal electrodes 1 and 3. FIG. 8D illustrates, like FIG. 8C, distances or displacements but now in the plane passing through diagonal electrodes 2 and 4. FIG. 9A illustrates the displacement relationships corresponding to the ideal case of good closure and planarity. FIG. 9B illustrates the case corresponding to poor closure between four adjacent displacements. FIGS. 9C and 9D illustrates the case where good closure but a lack of planarity may result in several possible combinations of displacements and corresponding planes. FIG. 9E illustrates the relationship between four possible combinations of displacements and their corresponding planes. FIG. 9F illustrates some additional planes which may result when diagonal displacements are combined as possibly corresponding displacements. FIG. 10A illustrates how three-dimensional projections of vectors relative to the four pads of the borehold tool may be transformed into two dimensions such that the density of vectors in a given area in the three-dimensional projection is not changed in the two-dimensional transformation. FIG. 10B illustrates one method of dividing the two-dimensional transformation shown in FIG. 10A into a classification system oriented relative to the position of the pads on the borehole tool, the position of magnetic North and the top side of the borehole. FIG. 11A illustrates the two-dimensional transformation when represented as an array of individual counters oriented to the tool, each counter or cell having a unique address which may, in one form, be considered as indices I and J. FIGS. 11B and 11C show how a finite vector falling in one counter or cell may be smeared from its particular counter into adjacent counters. FIG. 12 illustrates a two-dimensional graphic display corresponding to the two-dimensional transform which may be produced as one feature of the invention. FIG. 13A shows a sequence of displacements obtained from correlations between various pairs of four signals and illustrates zones containing sequences of displacements indicated to be stable for various possible combinations of displacements. FIG. 13B illustrates how diagonal displacements and their corresponding diameters can be combined and resolved as tangent vectors. FIG. 14 illustrates in numerical form sequences of displacements containing zones of stable sequences and adjacent stable sequences which have been determined from displacements obtained by correlating pairs of signals derived from adjacent sources. FIG. 15A illustrates some preliminary steps in the procedure used to obtain sequences of displacements and corresponding quality, diameter and inclinometer information. FIG. 15B illustrates detailed steps in the procedure to determine substantially stable sequences of displacements. FIG. 15C illustrates a procedure to determine pairs of adjacent stable sequences. FIG. 16 describes a step in a procedure to automatically determine the starting and ending boundaries of zones of adjacent pairs of substantially stable sequences. FIG. 17 illustrates the steps of a program corresponding to the procedure illustrated in FIG. 16. FIG. 18 illustrates in detail the steps of the procedure to combine corresponding displacement to produce functions representing the angular relationship between the displacements. FIG. 19 illustrates the detailed steps in a procedure to classify combinations of displacements produced in the process illustrated in FIG. 18. FIG. 20 illustrates the detailed steps of a procedure to analyze classified combinations of displacements to determine the positions of various classes and the relative position of the dominant class. FIG. 21 illustrates the detailed steps of a procedure to determine the relative position of features in each signal interval corresponding to the dominant class determined as illustrated in FIG. 20. FIG. 22 illustrates the improvement obtained in the determination of formation dip and azimuth measurements when techniques of the described invention are applied. FIG. 23 illustrates certain relationships useful in determining when a source of a signal is displaced from the borehole wall. FIGS. 24A and 24B illustrate the determination of a meaningful diameter in non-circular holes. TABLE I, shown at FIG. 25, illustrates certain relationships between known displacements and equivalent orthogonal displacements. TABLE II, shown at FIG. 26, illustrates displacement ratios corresponding to various signal sources or pads. TABLE IIIA, shown at FIG. 27 shows by example tabulations of stored cell addresses, cell contents and other entries which may be produced by the process illustrated in FIGS. 19 and 20. TABLE IIIB, shown at FIG. 28, shows by example the results of the processing illustrated in FIG. 20 when applied to the example of TABLE IIIA. TABLE IV, shown at FIG. 29, shows by example the cell addresses corresponding to the position of clusters of cells or classes of varying rank. Referring now to FIG. 1, there is illustrated a method of acquiring and processing signals obtained from a borehole investigating device commonly known as a dipmeter. This device is described in one form in U.S. Pat. No. 3,521,154 issued July 21, 1970 to J. J. Maricelli. The purpose of the dipmeter device is to obtain signals from three or more radially spaced sources usually in the form of pads which contact the borehole wall. Signals obtained from such sources reflect formation features at their intersection with the borehole wall and are useful in determining the orientation of the formations penetrated by the borehole. Typical earth formations are represented by the shale formations 13 and 14 shown in FIG. 1, and intervening sand formation 15. Typical formation features are boundaries 16 and 17 shown between these formations. As shown in FIG. 1, the borehole apparatus 18 is lowered on cable 30 into a borehole 10 for investigating the earth's formations. The downhole investigation device 18 is adapted for movement through the borehole 10 and as illustrated, includes four pads designated 19, 20, 21 and 22 (the front pad 19 obscures the view of back pad member 21 which is not shown). The pad members 19 through 22 are adapted to derive measurements at the wall of the borehole. Each pad includes a survey electrode shown as Ao. One of the pads, herein designated as pad 19, may contain an additional survey electrode Ao' useful in determining the speed of the tool. Each survey electrode is surrounded by an insulating material 48. The insulating material and thus all the survey electrodes are surrounded by a main metal portion 45 of the pad. The metal portion 45 of each pad, along with certain other parts of the apparatus, comprise a focussing system for confining the survey current emitted from each of the different survey electrodes into the desired focussed pattern. Survey signals representative of changes in the formation opposite each pad are obtained from circuits comprising Ao electrodes, focussing elements, and a current return electrode B shown in FIG. 1. The upper end of the borehole tool 18 as shown in FIG. 1 is connected by means of an armored multiconductor cable 30 to a suitable apparatus at the surface for raising and lowering the downhole investigating device through the borehole 10. Mechanical and electrical control of the downhole device may be accomplished with the multiconductor cable which passes from the downhole tool 18 through the borehole to a sheave wheel 31 at the surface and then to a suitable drum and winch mechanism 32. Electrical connections between various conductors of the multiconductor cable, which are connected downhole to the previously described electrodes, and various electrical circuits at the surface of the earth are accomplished by means of a suitable multi-element slipring and brush contact assembly 34. In this manner, the signals which originate from the downhole investigating device are supplied to the signal processing circuits 39 which in turn supply the signals to a signal conditioner 40 and recorder 41. A suitable signal generator 42 supplies current to the downhole tool via transformer 50 and to signal processing circuits located at the surface. More details of such circuits are described in the aforementioned Maricelli patent. Signals obtained from the downhole device may be recorded graphically by a film recorder 41. One such recorder is described in U.S. Pat. No. 3,453,530 issued to G. E. Attali on July 1, 1969. In addition, the signals may be processed to obtain discrete samples and recorded on digital tape. A suitable digital tape recorder is described in U.S. Pat. No. 3,648,278 issued to G. K. Miller, et al on Mar. 7, 1972. The signals may be sampled by driving sampling devices, such as those described in the above-mentioned digital tape recorder, by the cable motion as measured at the surface. For example, the cable length measuring wheel shown as 34A in FIG. 1 may be used in controlling the signal processing, sampling and recording subcycles as indicated by signal line 34B. Therefore, each sample of a measured signal corresponds to one increment in depth and displacements determined between such sample signals are indicative of depth displacements. The dipmeter signals or samples thereof may also be transmitted directly to a computer. The computer may be located at the well site or the signals may be transmitted via a transmission system to a remote computer location. One transmission system which may be used is described in U.S. Pat. No. 3,599,156 issued to G. K. Miller, et al on Aug. 10, 1971. The recorded or transmitted signals may be processed as digital measurements by general purpose digital computing apparatus properly programmed in a manner to perform the processes described herein or by special purpose computing apparatus composed of modules arranged to accomplish the described steps to accomplish the same process. Alternatively, as shown in FIG. 1, the signals may be processed directly at the well site, using conventional digital computing apparatus 60 when properly programmed and interfaced to the signal conversion means 52. One such computing apparatus is the Model PDP-11/45 obtainable from the Digital Equipment Corporation. Suppliers of such equipment may also supply signal conditioning circuits 40 and signal conversion means 52 suitable for conditioning and converting analog signals to digital samples for subsequent digital storage and processing. Further, such computing apparatus ordinarily includes a memory for storing data and information such as parameters, coefficients and controls used and generated by the processing steps. A brief description of one process which may be performed at the well site by such a computer 60 when properly programmed is illustrated by Blocks 62 through 102 of FIG. 1. Other processes will be described in detail in relation to additional FIGS. 15A through 21. Blocks 62 through 102 of FIG. 1 illustrate the steps of correlating the dipmeter signals in pairs to obtain sequences of displacements between similar features on the signals, determining a zone of displacement sequences which is suitable for subsequent combination and analysis, combining and classifying all the possible corresponding displacements in this zone and perhaps, as indicated in Block 102, outputting these classifications at this time. However, these classifications may be automatically analyzed to locate the dominant mode for these classifications and, if found, the location of this mode may also be output as indicated by Block 98. This location is indicative of the dip and azimuth of the formation features in the zone. Processing may then continue with more correlations if needed and the determination of more displacement zones to be processed. When performed at the well site, it may be desirable to record and/or display the results of such processing on recorder 110 connected to the programmed digital computer 60. Recorder 110 may be a digital tape recorder or have display capabilities such as a printer, plotter or CRT recorder. The nature and use of these devices is well known and will not be described herein. Referring again to FIG. 1, a more detailed description will now be provided for the process shown there in the form of the steps of a process flow diagram, and which may be performed with the aid of the digital computer 60 programmed in accordance with this invention. After signal conversion 52 and storage in the memory of the computer 60, signals may be read from memory and correlated by pairs to determine possible displacements between corresponding features on the signals as indicated in Block 62. The correlation process is well known, but in review, includes successively comparing identical length intervals equal to the correlation length 64 of two signals. At each comparison, the interval on one of the signals is displaced by a given displacement from the corresponding interval on the other signal. Successive comparisons and displacements produce a series of correlation values known as a correlogram. These values are compared to determine the displacement indicating the position at which similar features present on both signals correspond. The above-described process is again repeated for a different interval of both signals using the same correlation length. This interval is located one correlation step 66 from the previously correlated interval. Another correlogram and displacement is obtained for this interval and similarly for a sequence of intervals spaced apart by one correlation step 66. In like manner, the same signal is correlated with other signals and the other signals correlated by pairs within themselves to produce additional displacements for the same interval. Thus one interval or sequence produces many displacements between the various signal pair combinations. For example, in the four pad dipmeter shown in FIG. 1, six displacement per sequence may be obtained. In the prior art techniques of correlation, the relationship between the correlation step and the correlation length is such that the correlation step 66 may be equal to the correlation length 64. Then each correlation sequence considers a new correlation interval on each pair of signals with the result that the displacements determined for each sequence of correlated intervals are essentially independent of each other. Most prior art correlation techniques include the ability to change both the correlation length 64 and correlation step 66. In performing the present invention, it is preferred that the correlation step may be made to be equal to less than one-half of the correlation length. In this way, sequential correlation intervals may be made to substantially overlap each other. In accordance with this invention, it is expected that the displacements determined from sequences of such substantially overlapping correlation intervals will be somewhat consistent when a dominant feature is present on both signals throughout the overlapping interval. Thus, as illustrated in FIG. 1 and preferred in the present technique, the correlation step 66 should be substantially less than the correlation length 64 such that the correlation process employs substantially overlapping correlation intervals. For each sequence, the same basic signal interval is used to correlate with other signals derived from sources around and across the borehole. Thus one sequence produces a round of many correlations, correlograms and displacements. Point A indicated at 70 in FIG. 1 corresponds to the beginning of an optimal procedure to determine a zone of displacements suitable for the analysis which follows beginning at Point B, designated as 74 in FIG. 1. However, as indicated by the dashed Branch 73, this procedure may be bypassed and a specified number of sequences, ten, for example, used to define a zone. In such a case, this number is related somewhat to the amount of overlap in successive sequences. For example, since at least a 50% overlap is preferred, at least two sequences are required to define a zone. Similarly, when a 75% overlap is used, four sequences could define a zone. A common problem in statistical techniques is to determine a significant sample group so that the results of the statistical anaylsis may be meaningful. In the previously described statistical techniques, the selection of the zones to be averaged or plotted in the prior art analysis may be arbitrarily determined as, for example, any given one hundred feet of dipmeter results. Or, for another example, the zones selected may be limited to depths corresponding to the boundaries of a known geological formation. As an additional example, dip and azimuth values may be compared to detect specified dip and/or azimuth related trends as previously discussed, with the limits of the trend establishing the zone. As indicated in Block 72 of FIG. 1, the zoning determination of the present technique is based upon comparison of displacements rather than dip and azimuth values. Briefly, the sequence of displacements determined between a given pair of signals are examined to determine stable sequences of displacements. Then, related pairs of displacement sequences are examined to see if stable sequences are present for corresponding displacements. The limits of such stable sequences of corresponding displacements determine the limits of a stable zone. The limits of the stable zone are then used to group the displacements into zones for subsequent analysis. A more detailed description is provided in regard to FIGS. 15A through 18. Then, beginning at Point B of FIG. 1, and as indicated at Block 76, possible corresponding displacements from each zone are combined and the resulting combinations classified in a classification system which is oriented relative to the position of the sources of the corresponding signals, i.e. the pads located on the dipmeter tool. Details of these procedures are provided in regard to the description of FIGS. 19 and 20. As indicated by the test in Block 80 of FIG. 1, this process continues as the test indicated in Block 80 will answer YES until all possible combinations of displacements have been combined and classified. At this time, the test indicated in Block 80 answers NO, and the process continues at Point C to begin the analysis of the classified combinations. As an optional feature, as indicated by the dashed Branch 100 of FIG. 1 and output Block 102, the classified combinations of displacements which resulted from the previous processes may be output at this time and recorded on recorder 110. FIG. 12, which will be described in more detail later, is illustrative of such output. It will be appreciated by those skilled in this art that any graphic output similar to that illustrated by FIG. 12 is of value in determining the relative position of the formation features represented by the displacements. It will be further appreciated that the positions represented by the various subdivisions of the classification system may be calibrated in terms of the apparent dip and azimuth values relative to the orientation of the tool as illustrated in FIG. 10B and as such may be converted into approximations of the actual formation dip and azimuth. Therefore such output, whether it be in the form as illustrated in FIG. 12, in tabular form, or other forms to be described, or the like, the results of the classified combinations is considered to be a significant feature of the present invention. It is a further feature of the present invention to automatically analyze classified displacements combinations. Such analysis determines the position of the dominant mode for the distribution of the classified displacement combinations and, if desired, accurately determines the dip and azimuth values of each sequence corresponding to each class or distribution mode. Still further, when successive sequences indicate dips varying by a few degrees, the corresponding combinations may be pooled to provide compensation for small inaccuracies causing the variation, thereby providing more accurate dip and azimuth values. Briefly, the analysis process indicated in Block 92 of FIG. 1 comprises comparing the number and/or quality of displacements combinations corresponding to each division of the classification system to locate the highest concentration or density of combined displacements. Where several concentrations or clusters of combinations occur, they are ranked to determine the dominant one. Once such a dominant cluster is located, displacement combinations from each sequence which contributed to the dominant cluster may be retrieved and utilized in the computation of dip and azimuth values corresponding to that sequence. For sequences having no displacement combinations which contributed to any of the clusters, or where no distribution modes or clusters are found within the zone, no reliable displacement combinations are considered to exist so no dip or azimuth computation is attempted. The analysis process will be described later in greater detail in regard to FIGS. 19, 20 and 21. Referring again to FIG. 1, optional Branch 106 corresponds to the case where only the output of the classifications as illustrated in Block 102 is desired and the analysis step illustrated in Block 92 is bypassed. As illustrated in FIG. 1, the process would continue in this case as it would if the analysis indicated in Block 92 has been performed. Of course, in this case where no analysis was made, no mode will be found and the test indicated in Block 94 will answer NO, so that the process continues as indicated by Branch 96, returning to Point A to begin again the zoning process previously described. Normally, the analysis of the classified combinations of displacements to locate the dominant mode as indicated in Block 92 of FIG. 1 is performed. However, as will be explained later in detail, it is possible that no mode or cluster will be located, in which case the test indicated in Block 94 will answer NO and the process will continue via Branch 96 as previously described in the case of the option where no analysis was performed at all. However, in the cases where the analysis is performed and is successful in locating a dominant mode, the test indicated in Block 94 answers YES and output of the mode location takes place as indicated in Block 98. This output may be in many forms, the simplest of which would correspond to the utilization of the recorder 110 to list the location of the dominant mode. As will be appreciated by those familiar with this art, and as illustrated in regard to FIG. 12, a knowledge of the mere location of the dominant mode is of significant value. As previously discussed in regard to the output of the classified combinations--as indicated in Block 102--such a location may be converted by well-known techniques into accurate dip and azimuth values. In more sophisticated form, a location of the dominant mode may be converted in conjunction with its output using the above mentioned techniques to a corresponding dip and azimuth value. In a still more sophisticated technique described later in detail in regard to FIG. 21, displacement combinations which contributed to the dominant mode or clusters or perhaps to lesser modes and therefore have a corresponding location, are retrieved and utilized in well-known techniques to produce dip and azimuth values for each sequence. These values may be output in conventional form such as illustrated in FIG. 22. Since these values benefit from the classification analysis process, improvement in accuracy for these values is significant over the prior art techniques, as illustrated in the comparison provided in FIG. 22. Further, since displacement combinations not corresponding to the dominant mode are not used to produce dip and azimuth values, the number of extraneous dips is reduced, adding to the significance of those which are produced. Still further, since stray displacements are not averaged in with good displacements, the accuracy of the dips produced is improved. In the case of the type of output illustrated in FIG. 22, the recorder 110 shown in FIG. 1 could be of the conventional X-Y type. However, the recorder 110 may easily serve as an intermediate storage facility in such a process, as for example, as a digital tape recorder of the type previously mentioned. The well-known graphic conversion steps are performed in subsequent processing at a later time. Or, in the case where transmission facilities to remote locations are employed, the required processing and recording of the usual output may be done at a different time and location. Thus, in review, FIG. 1 illustrates the measurement of geophysical signals at sources, here corresponding to dipmeter pads spaced at different radial positions around the borehole. These measurements are acquired and correlated to produce displacements representative of the position of formation features reflected in the correlation interval. These displacements may be used to determine zones of stable or unstable displacements. More particularly, sequences of displacements are divided into groups of displacement for later analysis. This division may be at points where changes in stability of the displacements is indicated, thereby forming sample groups of displacements corresponding to stable and unstable zones. Where prior art techniques combine the two best corresponding displacements in each sequence, discarding the extras, the present invention combines all possibly corresponding displacements produced from the round of correlations from each sequence. Corresponding displacements from individual sequences within these zones are combined and classified in the classification system, which in the illustrated case, is oriented to the pads of the dipmeter tool. The analysis of the classified combinations of displacements locates the position of the dominant cluster of combinations and this location also may be used to determine the relative position of the signal features corresponding to the displacements. When the technique is applied to dipmeter signals such a position may be converted to the dip and azimuth of formation characteristics at their intersection with the borehole wall. Referring now to FIG. 2, a brief description will be given of how certain reference information characterizing the position of the borehole tool and therefore the sources of the signals is measured. Incorporated within the apparatus 18 shown in FIG. 1 is an inclinometer system, schematically illustrated in FIG. 2. The inclinometer system is referenced to one of the signal sources, usually the pad designated as No. 1. The inclinometer system is composed of two related measuring systems. One system contains a pendulum 120 suspended in relation to the center line or axis of the borehole tool such that it establishes a vertical plane in which to measure the deviation angle .delta. of the borehole tool. This may be done as illustrated in FIG. 2, for example, by measuring with a second pendulum and a potentiometer 122, the angular deviation of the tool axis from this vertical pendulum. This deviation is sometimes known as the drift angle. The first pendulum 120 is also related in a rotational sense to the position of the reference pad. An additional potentiometer shown as 124 in FIG. 2 may be used to measure the rotational angle .beta. between the reference pad and pendulum 120 position. This angle .beta. is usually measured from the high side or the top of the hole and is known as the relative bearing. It is conventional to measure this angle such that it has a positive sign when measured clockwise from the high side of the hole to pad No. 1. An additional system incorporates a magnetic compass 130 and another potentiometer 132 such that the potentiometer measurement reflects the angle by which the referenced pad differs from magnetic North as measured by the compass 130. As shown in FIG. 2, this angle .mu. corresponds to the azimuth of the number 1 pad. Thus, it may be seen how the position of a reference point on the tool, here shown as pad No. 1, may be related both to magnetic North, as expressed by its azimuth, and to the top of the hole, as expresssed by its relative bearing and deviation angle. It is readily apparent then that any measurement which is referenced to the position of pad No. 1 may be also referenced to the top of the hole or to magnetic North which of course may be converted to geographic North. Still further, it will be apparent how the position of the top of the hole and magnetic North may be referenced to pad No. 1. It is well known how to use these reference measurements. Further details may be obtained, for example, in the aforementioned Moran, et al paper, particularly in the appendix thereof. Referring now to FIG. 3, there are illustrated the four pads of the dipmeter tool shown in FIG. 1, designated here as 1, 2, 3 and 4. As the dipmeter tool 18 moves up the borehole 10, the four pads each trace a path on the borehole wall as indicated in FIG. 3 by the dashed vertical lines. These paths will intersect the plane of a formation feature at the borehole wall at the four points indicated by small circles 1 through 4. Further, the nature of the pad suspension system for the dipmeter assures that these paths trace opposite sides of the borehole for each diagonally opposing pair of pads, for example, pad pairs 1 and 3, or 2 and 4. The signal response for each of the four pads is shown in FIG. 3 as S1 through S4. The change in the character of the signals corresponding to the feature which intersects the borehole is shown as signal features f.sub.1 through f.sub.4. When the plane of the feature is inclined relative to the borehole as shown in FIG. 3, there will be a displacement between the corresponding features on each signal. As shown, one pad will respond to the feature first as the tool is withdrawn from the borehole, with the opposite pad responding last. In FIG. 3, these pads correspond to Pads 3 and 1, respectively. The correlation process which, of course, compares the similarity of two signals, may then be used to determine the displacement between the points of intersection of the feature with the paths of the pads along the borehole wall. For example, the correlation of S1 and S2 determines the displacement between Points f.sub.1 and f.sub.2. As illustrated in FIG. 3, Pad 2 intersected the feature plane at a deeper depth than Pad 1. Thus, the depth of the f.sub.1 on S1 is less than the depth of f.sub.2 on S2. By convention, the displacement between S1 and S2 is therefore considered to be negative. This is consistent with the notation that the displacement between two signal features equals the depth of the feature on the signal from the first pad minus the depth of the feature on the signal from the second pad. As shown in FIG. 3, the displacement between intersection point for the feature at f.sub.1 on S1 and f.sub.2 on S2 is designated d.sub.1-2 and as shown, is negative, since f.sub.1 is above f.sub.2. More details as to conventions will be given in regard to FIG. 8A. Three additional displacements similar to that obtained between the adjacent Pads 1 and 2 may be obtained by correlating S2 with S3, S3 with S4 and S4 with S1. Thus, the four adjacent displacements are designated accordingly, as d.sub.1-2, d.sub.2-3, d.sub.3-4, and d.sub.4-1. Two additional displacements may be obtained to complete a full round of displacements for this level or sequence by correlating the signals obtained from diagonally opposing pads. In the case of the four-pad tool illustrated in FIG. 3, these diagonals correspond to d.sub.1-3 and d.sub.2-4. Thus, for the illustrated four-pad tool, there are six possible displacements which may be obtained by correlating the four signals. There are, of course, other dipmeter tools which may have different numbers of pads, for example, the three-pad tool from which, because of the 120.degree. angular relationship between the pads, no diagonal displacements may be obtained. It is well known that the position of any three points provide the definition a plane, which in the dipmeter art is expressed as the depth, dip and azimuth of the plane. Of course, in addition to the above described displacements between signal features, the radial distance between the measure points on pads corresponding to these signals, is also needed to define the required three points. In the four pad tool, these radial distances are obtained from the two diameters measured between opposing pads. Thus, any two related displacements and corresponding diameters define the three points and may be used to produce a dip and azimuth value. Even in the three-pad configuration, where there are only three possible displacement determinations, an extra displacement is apparent, and in fact, three different combinations of displacements pairs are possible, providing the redundancy of three different azimuth and dip determinations. In the illustrated four-arm dipmeter tool, where six displacement determinations are possible along with two separate diameter measurements; i.e., along the diagonals 1-3 and 2-4, a multiplicity of combinations exist and, as will be explained later, provide the possibility of up to thirteen different dip and azimuth values. Ideally, all of the above multiplicity of possibilities would yield the same dip and azimuth value. Unfortunately, limitations inherent to the correlation process and to the measurement environment in the borehole provide ample opportunity for one or more of the combinations to be in error. FIGS. 4A and 4B illustrate one type of measurement problem which may occur in deviated boreholes such as commonly occur in offshore drilling. Referring now to FIG. 4A, there is shown an illustration of the four-pad tool in one possible orientation the tool may take when the borehole is substantially deviated from vertical as illustrated in the corresponding FIG. 4B. In such a situation, the substantial weight of the dipmeter tool tends to collapse the mechanical assembly of the weight supporting diagonal pair of pads. In the illustrated case, these pads are shown as topside Pad 1 and downside Pad 3. In effect, the pad on the downward side of the hole tends to carry a substantial portion of the weight of the tool. This abnormal load may act on the caliper linkage supporting the opposing topside and downside pads to collapse this linkage independent of the linkage for the other pads. The result of such a collapse, even though only slight, is that the pad on the top side of the borehole loses its contact with the borehole wall. Recall now that the two opposing pad pairs have two corresponding diameter measurements D.sub.1-3 and D.sub.2-4 as shown in FIG. 4A. In many cases, the tool collapse condition is indicated by one of these diameters being somewhat less than the other diameter, for example, as shown in FIG. 4A, D.sub.1-3 is less than D.sub.2-4. Unfortunately, this relationship is not conclusive as indicating the collapsed condition. Further, as boreholes are frequently elliptical, the different measurements may correspond to accurate "diameter" measurements in such cases and in fact all pads are in contact with the wall. Further, as shown in FIG. 4A, neither of the diameter measurements may correspond to the actual diameter D.sub.e even in a circular hole in the substantially deviated hole case. As shown in FIG. 4B, the pad on the top side of the hole may "float" at a substantial spacing from the borehole wall. Here this spacing is designated as .DELTA.D and corresponds approximately to the difference between the measured diameter D.sub.1-3 and the effective diameter of the borehole D.sub.e. Recall now that the electrode arrangement on the dipmeter tool is designed to focus the current emitted from the Ao electrode. Since the resulting current path is substantially normal to the pad face, it will be appreciated then that such focussing may overcome the effect of loss of contact of the floating pad with the borehole wall, as far as at least some of the response to the formation features is concerned. In fact, in well-focussed tools, the ability to overcome substantial pad-to-wall separation is well known and some skilled in the dipmeter art often add a small given distance to the caliper measurement in the belief that the pad responds as if it was located a small distance within the formation. Unfortunately, there is no way to directly measure the effective distance between opposing pads, such as diameter D.sub.e. Further, in the prior dipmeter art, no appreciation is given for the fact that the effective diameter for the floating pad response is not directly related to the diameter corresponding to the caliper measurement. Since the focussed response in effect extends the floating pad to the intersection point of the formation feature with the borehole wall, the correct diameter, in this case, may equal the borehole diameter illustrated as D.sub.e in FIG. 4B. A serious dip computation error occurs if the pad separation .DELTA.D is not recognized and considered appropriately. Further, all displacements determined from signals obtained from the displaced or floating pad are affected. As is apparent from FIG. 3, three out of the six displacements normally available from a four-pad tool are so affected. Since the diameter associated with the collapsed caliper and floating pad is also involved in the dip computations as will be explained later, it is possible that three-fourths of the resulting dips may be affected. For a given feature inclined relative to the borehole, the larger the borehole diameter, the greater will be the corresponding displacements. Thus, if a measured diameter which is too small compared to the effective diameter is used, resulting dip will be too high. It will now be appreciated from the foregoing explanation, that the displacements associated with a signal obtained from a floating pad will appear to be exaggerated when compared with the displacements obtained from other pairs of signals. While such exaggerated displacements are indicative of the floating pad situation, they are not unique to this situation. Referring now to FIG. 5A, there are shown the four signals which may be obtained from the four-pad tool. The signals designated S2, S3 and S4 are very similar and each contain a common feature labeled B, C and D on each of the signals respectively. The signal designated as S1 contains not only this feature, here designated as A, but an additional feature designated as A'. Thus, as illustrated, there is a question as to whether the Feature A or A' corresponds to the unique Features B through D on the other signals. As illustrated in FIG. 5A, unique Features B, C and D accurately and unambiguously define plane B-C-D. However, when Feature A is taken in combination with B and D, plane A-B-D is defined while with Feature A', a different plane A'-B-D is defined. Still further, when the Features on S1 are taken in conjunction with B and C, two additional planes, A-B-C and A'-B-C are defined and similarly in conjunction with C and D, planes A-C-D and A'-C-D are defined. FIG. 5B illustrates the correlograms corresponding to the correlations of various pairs of the signals illustrated in FIG. 5A. For example, Correlogram 1-2 represents a function expressing with increasing amplitude, increasing similarity between the two signals, S1 and S2. This function is evaluated as the two signals are displaced relative to one another. As indicated on the displacement axis and consistent with the previously mentioned depth relationship, the displacement would be negative if the corresponding feature on the first signal was above the feature on the second signal. Similarly, the displacement would be zero if the feature occurred at equal depths and positive if the feature occurred at a deeper depth on the first signal than on the second. Thus, for the correlogram labeled 1-2 corresponding to the correlation of S1 with S2, the correspondence of Feature A with Feature B on Signals S1 and S2 respectively is more negative than the possible correspondence with Feature A' on S1 with Feature B. As is illustrated with the S2 to S3 correlogram, i.e. Correlogram 2-3; where little ambiguity exists that Feature B corresponds to Feature C, a single peak indicated as B-C corresponds to the displacement. However, as indicated on each of the correlograms involving Signal 1, where two similar features, A and A' exist, there are two peaks which may more or less resemble each other, at least in amplitude, such that the displacements selected by detecting the maximum amplitude as the best correlogram likeness, might select either the A or A' feature as corresponding to the similar feature on the other signals. If, as illustrated, for example, the Feature A is the feature which actually corresponds to B, C and D on the other signals, then selecting displacements corresponding to A' would represent a miscorrelation. While it may be apparent to those skilled in this art that A is more similar than A' to Features B, C and D, such mis-correlations do in fact occur and, as is readily apparent from FIG. 5A, lead to displacements which, when combined with other displacements, define a plurality of additional planes. Still further, when they do occur, comparison of the displacements would find some of the displacements were exaggerated as compared to others, and in this sense, ambiguous with the use of this diagnostic to detect the floating pad situation. The exact nature and shape of the correlogram depends somewhat upon the correlation function selected. Therefore, the correlograms illustrated in FIG. 5B are not necessarily representative. FIGS. 6A through 6E illustrate in a simplified fashion a possibility for a mis-correlation which is considerably less dependent upon the nature of the correlation function and the shape of the resulting correlogram. Referring now to FIG. 6A, there is shown the condition where two actual features, A and B, are present in the same correlation interval on Signals 1 through 4. However, in one sector of the hole, Feature A is better defined than Feature B, and in the other sector of the hole, the reverse is true. This variation in definition may be real, as for example, the sharpness of a bed boundary varies, or it may be artificially induced by a measurement problem such as the floating pad problem previously described. For simplicity, both Features A and B are illustrated as intersecting the borehole at zero dip; i.e., no inclination relative to the borehole, so that no displacement occurs between the actual corresponding signal features. Irrespective of the correlation function employed, and as will be appreciated when considering only two of the curves shown in FIG. 6A at a time, the presence of two similar features in the same interval has the distinct possibility of confusing the feature corresponding to A on one signal with the feature corresponding to B on another signal. This is particularly true when the actual corresponding signal feature is suppressed on one or both signals as may occur when these signals were obtained from substantially different sectors of the borehole. In the prior art practice, this may be further complicated by discarding what may be the correct correspondence but, unfortunately, also the poorest quality correlation. When correlating the Signal 1 with the Signal 2 shown in FIG. 6A, where there is little doubt that A corresponds to A on both signals, and when reinforced by even weak agreement in regard to Feature B, the correlation function produces a distinct peak as shown in FIG. 6B as Correlogram 1-2. Consequently, the displacement d.sub.1-2 is accurately selected and corresponds to A with A and B with B on both signals. However, as illustrated in this correlogram, there is some evidence that A on Signal 1 could correspond with B on Signal 2 and somewhat less evidence that B on Signal 1 might correspond with A on Signal 2. When correlating Signals 2 and 3, again the combined effect of A with A and B with B, as illustrated by Correlogram 2-3 in FIG. 6C, produces the correct displacement d.sub.2-3, but now there is a distinct possibility that A on Signal 2 could be B on Signal 3, as indicated by the somewhat narrower but relatively large peak on the lefthand (-) side of Correlogram 2-3. As illustrated in Correlogram 3-4 shown in FIG. 6D, the strong similarity of Feature B on both signals S3 and S4 along with some similarity for Feature A combine to produce a distinct peak on the correlogram at the correct displacement d.sub.3-4. Since A on one signal does not resemble B on the other signal, the peaks corresponding to this conflict are not significant. In this case, the correlation function can be said to be dominated by Feature B, with little contribution from Feature A. However, as illustrated in FIG. 6E, when correlating Signal 4 with Signal 1, there is the distinct possibility that Feature B on Signal 4 corresponds with Feature A on Signal 1. This is illustrated by the large peak designated as B.sub.4 -A.sub.1 on the correlogram which results in the large positive displacement d.sub.4-1. This erroneous displacement resulted from the suppression of Feature A on Signal 4 at the same time as Feature B was suppressed on Signal 1. Similarly, in FIGS. 6F and 6G, where the correlations are across the borehole and the signals were derived from opposing pads, a substantial difference may exist in the actual characteristics of the signals. As illustrated in FIG. 6F, there is a strong resemblance between Feature A on Signal 1 and Feature B on Signal 3, resulting in a large negative-displacement peak on correlogram 1-3 and an incorrect displacement d.sub.1-3 being determined. Of course, there is still a peak but of lesser amplitude corresponding to the combined effects of Features A and B on both signals which does indicate the correct displacement. As illustrated in FIG. 6G, the correlation between Signal 2 and Signal 4 is also influenced by the strong resemblance of Feature A on Signal 2 with Feature B on Signal 4 because Feature A is suppressed on Signal 4. However, because Feature B is found on both Signals 2 and 4, the correct d.sub.2-4 displacement is determined from the correlogram, but perhaps only marginally so. Thus, FIGS. 6A through 6G illustrate how erroneous correlations may result for at least some of the correlations between pairs of signals obtained over the same interval, particularly where both signals intervals include two or more features. The problem is further complicated when conditions tend to change the nature of the signal features in different sectors of the borehole, such as may occur when formation bedding planes intersect the borehole at substantial angles. Here, the possibility exists that the two opposing pads measure the focussed response of the tool to a bedding plane intersecting the borehole at high inclination angles, while the other opposing pads measure the focussed response with little inclination angle, resulting in substantial dis-similarities between adjacent signal pairs. These inclination angles may actually be produced by horizontal formations (of zero dip) which are penetrated by a highly deviated hole and when coupled with the possibility of a floating pad, present a complex analytical problem. The prior art practice of discarding all but the minimum required three related displacements is of course heavily dependent upon the ability to consistently pick the best three displacements, which usually are taken as those with the largest amplitude peaks (lowest minimums with some correlation functions). There are other methods of qualifying these best displacements in addition to the above, as will now be described, but as will be later appreciated, none can provide the necessary assurance that these three displacements, and only these three displacements, out of the multiplicity available, correspond to the only possible dip and azimuth measurements for a given sequence. There are several correlation functions which may be employed in the correlation process and, in general, each produces either a maximum or a minimum characteristic at the displacement position on the correlogram corresponding to the best likeness or similarity between the correlated signals. In addition, there are several methods of assigning a correlation quality factor to the correlogram characteristic which determined the displacement. In practicing the present invention, it is preferred that a quality factor be assigned to each displacement determination. This quality factor may then be used as an enhancement to the analysis procedure used in locating the dominant mode of the classified combination of displacements as will be explained later. However, in correlation methods where a quality factor is not available, a quality factor or weight of unity may be assigned. Referring now to FIG. 7A, there is shown the general characteristics of a correlogram derived from a well-known normalized correlation technique. This technique produces a correlation coefficient of unity when identical signals are correlated, which of course represent the maximum possible quality factor which can be expected. Where no similar features are present on the signals, the correlation coefficient of zero would be expected and where the features are equal but opposite, a correlation coefficient of minus one would be expected. It would be obvious from examining such a correlogram, as shown in FIG. 7A, that the best correlation corresponds to the maximum point A and in fact, the value of A may be used as the quality factor. The peak value of the correlogram could also be measured from some base line, such as the distance indicated as Q, and used as the quality factor. The peak value could also be measured relative to the next highest peak as indicated in FIG. 7A by .DELTA.C and used as a quality factor. Still further, and as is common in statistical distribution studies, the width W of the correlogram peak at some fraction of its total height, for example, at two-thirds Q, could be used as a quality factor. Still further, since as previously mentioned, the shape of the correlogram peak in regard to its sharpness may be significant, the angle .alpha. indicated in FIG. 7A which may be defined by the slope of the two sides of the peak could be used as the quality factor. In any case, it is preferred that some representation of the correlation function be used as a quality factor which allows the distinction between good correlations and bad correlations. As previously discussed in regard to the use of overlapping correlation intervals, it is significant to note the characteristics of correlograms obtained between successive correlations of the same two signals, particularly since the nature of the correlogram for successive correlations is implied in the stability of the displacements determined therefrom. When a single feature or a set of features having the same displacement relationship are present on both correlated signals, a large and distinctive correlogram is produced as previously described in regard to FIG. 6B. From this correlogram feature, an accurate displacement may easily be determined. For the next sequence, the correlation process is repeated for the same two signals over a different interval which, in addition to the previous features, may contain additional signal features which may or may not correspond. If the same distinctive peak and the same displacement determination result for this sequence, the corresponding features present in both correlation intervals are dominant over the new features present in the subsequent interval. Thus, if substantially the same displacement is determined in two sequential correlations over different but overlapping intervals, it implies that at least one dominant signal characteristic is present on both signals in the interval common to both correlations. Thus, a sequence of substantially stable displacements determined between two signals in a correlation process which uses substantially overlapping correlation intervals implies that the stable displacements correspond to dominant features present on both signals, rather than to less significant features present on one or the other signal which temporarily give rise to what might even be regarded as a good quality correlation. FIG. 7B illustrates one type of problem present in such sequence of displacement determinations. Shown are three correlograms obtained from adjacent overlapping correlation intervals on the same two signals which both contain at least one common feature within the interval. In Sequence 1, a large, relatively smooth peak is shown with the maximum value indicated at A which corresponds to the correct displacement. However, to the left or negative displacement side of this peak, is another peak B having a maximum value which is shown .DELTA.C.sub.1 less than A. Thus, the correct displacement at A may be only marginally distinguished from the erroneous displacement at B. In the next correlogram for Sequence 2 in FIG. 7B, the large smooth peak is still present at the same displacement. However, the large peak was not selected as indicative of the displacement because a relatively sharp but larger peak C was the maximum in this correlogram. Subsequently, in Sequence 3, this sharp peak is no longer the maximum, resulting in a displacement determination at A' which substantially is the same as the displacement determined in Sequence 1. Thus, FIG. 7B illustrates a temporary departure as, for example, for one sequence, of a displacement determination from the displacement values determined from previous and following sequences. Had it not been for the clearly erroneous displacement caused by a temporary sharp, high amplitude peak in Sequence 2, an essentially continuous sequence of substantially stable displacements would have been determined. It should also be realized that without the benefit of the overlapping correlations from Sequences 1 and 3, the displacement found in Sequence 2 could not by itself be judged as erroneous. FIG. 7C illustrates yet another problem in the use of correlograms. Here, an additional sequence of three correlograms obtained between the same two signals indicates a large peak which is well above the amplitude of any other peaks in each correlogram, but because of the lack of a unique top, results in a sequence of displacements which vary somewhat but this variation is much less than the differences in displacements that would result from picking different peaks in a sequence of correlograms, such as illustrated in FIG. 7B. FIG. 7C is typical of a correlation interval containing a number of corresponding features which vary in thickness or width. This lack of resolution is usually characterized in the correlogram by the presence of a number of secondary peaks superimposed on the general peak. In such a case, each displacement in the sequence differs only slightly from its adjacent sequence and the actual displacement probably corresponds to the average of the individual displacements determined from a sequence of such correlograms. Another variation of the type of problem illustrated in FIG. 7C but which is not illustrated herein is where a true slow change occurs in the actual displacement relationship between a series of features. In this case, the displacement determined will be found to also vary from sequence to sequence. The variation will usually be about the same degree and the same direction between each sequence. In such a case, there is nothing inaccurate about each displacement and such a sequence of displacements would be considered as stable, each displacement affirming its neighbors in the sequence. It should be noted that such slowly changing displacements may also be created by a dipmeter tool which is rotating as it is being moved through the borehole. FIG. 7D illustrates another valid characteristic in a sequence of correlograms. In Sequence 1, a distinctive peak results in a displacement determination at A which is repeated at substantially the displacement A' in Sequence 2. Then, in Sequence 3, a new but equally distinct peak results in a displacement determination at Point B. An examination of the sequence of correlograms usually finds in such cases that the peak corresponding to A in Sequence 1 and Sequence 2 is still somewhat present in Sequence 3. Similarly, the peak corresponding to B in Sequence 3 was present in the previous sequences also but to a lesser extent. This case illustrates, for example, the transition between two geological formations which actually have different dips corresponding to displacement A and displacement B, respectively. In such cases, these displacements should be considered separately in any subsequent analysis. From the foregoing, it will be seen that much can be learned about the nature of the correlograms themselves by utilizing the variation in displacements determined from sequences of substantially overlapping correlograms. Therefore, it is not essential in this invention to be able to examine the correlograms themselves. Thus, by examining displacements which may have been previously obtained from a separate process which did not retain any correlogram information other than the displacement and perhaps a correlation quality factor, much can be learned about the now unavailable correlograms. More particularly, a comparison of displacements determined in successive correlations between the same two signals may be used to separate displacements into groups for further analysis. When the separation of the groups is placed at the point where a substantial and permanent change in the displacements occurs, the displacement grouping has a high probability of corresponding to the actual formations themselves. As previously mentioned, the use of a correlation process is well known for determining displacements for a given interval. However, a brief review of some conventions will be provided to aid in explaining some features of this invention. FIG. 8A illustrates some conventions well known in the dipmeter art which will also be used here in the definition and processing of the displacements. In review, and by way of example, the case of the four-pad dipmeter is again illustrated. Recall now that the four electrodes on the dipmeter tool are maintained in a common plane normal to the axis of the borehole tool. As illustrated, this plane is shown as the electrode plane and contains electrodes 1, 2, 3 and 4 which are indicated by the solid circles in FIG. 8A. Also recall that these electrodes are maintained in a fixed relationship in this plane such that each pair of opposing electrodes, such as 1 and 3 or 2 and 4, is each equally distant from the axis of the borehole tool. It is convenient to regard depth as being measured from this electrode plane along the axis of the borehole tool and increasing downward as indicated in FIG. 8A by the Z axis. Thus, the distance between the actual electrode in the electrode plane and the point at which the electrode crosses the intersection of a dip plane may be measured in terms of depth along this Z axis. This point of intersection with the dip plane is illustrated as an open circle in FIG. 8A. The distance from the actual electrode to this intersection point is illustrated as z.sub.n where n corresponds to the electrode number. For example, the distance between the number 1 electrode on Pad 1 and the point where it will normally respond to the dip plane is designated as z.sub.1. As illustrated in FIG. 8A, distances from the electrode plane to the point of intersection with the dip plane for each electrode are designated as z.sub.1 through z.sub.4. These distances are related to the displacements determined between any two electrodes by the illustrated algebraic relationships. For example, d.sub.1-2 =z.sub.1 -z.sub.2. More particularly, the use of the electrode reference plane allows understanding of how displacements between different electrode pairs may be conveniently related in a general way. If, for example, and as can readily be seen in FIG. 8A: d.sub.1-2 =z.sub.1 -z.sub.2 (Eq. 1); and d.sub.2-3 =z.sub.2 -z.sub.3 (Eq. 2); then it will follow that d.sub.1-3 =z.sub.1 -z.sub.3 =(x.sub.1 -z.sub.2)+(z.sub.2 -z.sub.3)=d.sub.1-2 +d.sub.2-3 (Eq. 3). Thus, by assuming each z distance is measured between the same two planes, displacements determined from adjacent pairs may be used to compute additional displacements, as for example, the displacement d.sub.1-3 above. It is not necessary with the above concept that electrodes 1 and 3 need be, as illustrated, opposing electrodes. Further, the electrode plane merely serves as an intermediate reference plane in the displacement computation. The above-described concept is illustrated graphically in FIG. 8B where, as in FIG. 8A, both the electrodes and their intersection points with the dip plane are represented in relation to the Z axis. Here, the above-mentioned z distances are again indicated. Consider now the distances z.sub.1 and z.sub.3 as they would be viewed from a position looking along the line drawn between electrodes 2 and 4. Such a view is shown in FIG. 8C and may be considered as taken in the 1-3 electrode plane which of course also includes the Z axis. Electrodes 2 and 4 of course are superimposed in such a view, while electrodes 1 and 3 appear on a common line drawn through these superimposed electrodes and normal to the tool axis. The distance z.sub.1 appears in FIG. 8C as measured from the plane containing the actual electrodes at the point corresponding to electrode 1 and along the path of the electrode to its intersection point with the dip plane. Similarly, the distance z.sub.3 appears in the corresponding relationship with electrode 3 while distance z.sub.2 is superimposed on the tool axis. It is clear from this diagram that the position of intersection point for electrode 2 with the dip plane merely serves as an intermediate turning point or benchmark in determining the distance between the intersection points for electrodes 1 and 3. It is also apparent that with this distance, a displacement between the intersection points for electrodes 1 and 3 may be computed from Eq. 3 described above. However, as previously mentioned, this relationship assumes a planar surface for the dip plane. Therefore, the displacement computed as above may not correspond to the displacement determined by correlating the signals from electrodes 1 and 3. Consequently, displacements which are computed from such algebraic relationships between actual displacements, are regarded as virtual displacements and denoted herein by the symbol (v), as for example, d.sub.1-3.sup.v in FIG. 8C. An apparent dip angle, .theta., appears, again assuming the planar dip requirement, between the line connecting the intersection points for the non-adjacent electrodes and a line normal to the tool axis. For the 1-3 electrode intersection line shown in FIG. 8C, this angle is designated as .theta..sub.1-3.sup.v and may be computed from the virtual displacement d.sub.1-3.sup.v when taken with the D.sub.1-3 diameter measurement. The tangent of this apparent dip angle may be found from: tan (.theta..sub.1-3.sup.v)=d.sub.1-3.sup.v /D.sub.1-3 (Eq. 4) The above relationships may also be derived using the distance z.sub.4 which is not shown in FIG. 8C. However, because the displacement convention reverses the sign for symmetrically opposing displacements, as for example d.sub.1-2 =-d.sub.3-4 and d.sub.2-3 =-d.sub.4-1, the virtual displacement equation becomes d.sub.1-3.sup.v =(-d.sub.3-4 -d.sub.4-1). Similarly, FIG. 8D shows the same conditions in the plane common to electrodes 2 and 4. By a corresponding analogy, it can be seen that the distance z.sub.3 now appears along the tool axis and also serves as an intermediate point between z.sub.2 and z.sub.4 which allows the combining of adjacent displacements d.sub.2-3 and d.sub.3-4 to form an equation corresponding to Eq. 3 above. This equation is: d.sub.2-4.sup.v =z.sub.2 -z.sub.4 =(z.sub.2 -z.sub.3)+(z.sub.3 -z.sub.4)=d.sub.2-3 +d.sub.3-4 (Eq. 3A) Again, an apparent dip angle .theta..sub.2-4.sup.v appears between the line connecting the non-adjacent electrode intersection points and the line normal to the tool axis and may be found by an equivalent tangent relationship: tan (.theta..sub.2-4.sup.v)=d.sub.2-4.sup.v /D.sub.2-4 (Eq. 5). Here the symmetrically opposing displacements also provide an alternate expression for the 2-4 virtual displacement: d.sub.2-4.sup.v =-d.sub.4-1 -d.sub.1-2 It should now be apparent that through the use of such virtual displacements, perhaps even incorporating some of the symmetrically opposing displacements, virtual substitutes may be computed for cases where the actual displacements are missing or in doubt for use in comparison with the actual displacements. Further, by choosing orthogonal pairs (those at 90 degrees to each other) for such virtual displacements, such as those corresponding to the D.sub.1-3 and D.sub.2-4 diameters, standardized processing of displacements becomes possible because the actual displacements, which may not always be available, can be computed when required. It should be realized at this point that this invention and the above concepts apply not only to the illustrated four-electrode tool but also to dipmeter tools with only three electrodes and to tools with more than four electrodes. This concept of computing virtual displacements from combinations of two or more adjacent displacements applies in general to any array of electrodes or transducers which may be geometrically related, as for example, by assuming displacements measured between them correspond to the same planar feature. These computed virtual displacements also should not be confused with the coincidence that they correspond to actual possible diagonals as is the case in the four-pad tool used to illustrate the invention. Thus, virtual displacements, and in fact, orthogonal pairs of virtual displacements, may be computed from arrays with either an even or odd number of electrodes as long as their position relative to each other is known. The value of such pairs of orthogonal displacements, be they real or virtual, in processing and analyzing combinations of displacements will be further appreciated from the following figures. Refer now to FIG. 9A in which there is illustrated four points indicated by the numbers 1 through 4 between which two orthogonal displacements may be determined. As was mentioned in regard to the previous FIGS. 8A through 8C, it will be appreciated that the displacements between the adjacent electrodes may be used to compute these orthogonal displacements, here shown as 1-3 and 2-4. Of course, the actual displacements may be determined by correlating the signals obtained from the opposing pairs of electrodes, but for simplicity in the following explanations, only displacements determined between adjacent electrodes will be discussed. While it is admitted that the surfaces of geological formations may not in fact be planar, the plane serves as a useful reference for testing the relationships between two or more displacements. FIG. 9A illustrates the perfect case where all of the six displacements determined between signals derived from four illustrated points correspond to a perfect plane. In such a case, all displacements between each pair of signals indicate that the correlation process is dominated by a common feature and that this feature corresponds to a plane. Two tests may be used to illustrate the above common feature and planar characteristics. These tests are the closure and planarity tests. The closure test is a common practice in surveying and simply requires, as indicated by its name, that the given traverse must close. In displacement form, this requirement simply means that the sum of all of the displacements in any continuous traverse which starts with a given electrode and returns to this electrode must equal zero. For the illustrated four-pad tool and for the traverse around the adjacent electrodes shown in FIG. 9A, this requirement may be expressed as: d.sub.1-2 +d.sub.2-3 +d.sub.3-4 +d.sub.4-1 =0 (Eq. 6) When the sum does not equal zero, this sum is usually termed the closure error EC. The lack of closure error EC essentially indicates that the same signal feature controlled all the correlations from which the displacements were determined. Recalling FIG. 5A where two features A and A' were present on Signal 1, it should be realized that displacements corresponding to traverse A-B-C-D-A would close, as well as traverse A'-B-C-D-A' would close. If, however, the correlation between S1 and S2 was controlled by A because Feature B more resembled A and the correlation between S4 and S1 was controlled by A' because Feature B more resembled A' such that the complete traverse corresponded to A-B-C-D-A', a closure error corresponding to A-A' would result. The fact that this traverse would not close reflects the fact that two different features, here A and A', were involved, and of course, in such cases planarity has no meaning. Referring now to FIG. 9B, there is illustrated the effect of a closure error EC. Here, in regard to Point 3, a gap equal to EC appears along one of the diagonals here illustrated as the 1-3 diagonal with the closure error appearing between Points 3 and 3'. However, it will be appreciated that there is no way of fixing the exact location of the closure error. Of course, if the closure error cannot be assigned to one of the displacements, none of the displacements may be used with assurance to determine even one plane, and in effect, planarity is undefined. When four or more displacements are obtainable, as for example, in the illustrated four-pad tool, and these displacements indicate good closure, it is then possible to test for planarity. The planarity test may be expressed in a number of ways. However, it is convenient to use the expression that reflects the expectation that the opposing displacements between the two orthogonal diameters should be equal and opposite, such as shown in FIG. 9A. Recalling the previously established conventions in regard to the sign for the displacements, this expression may be formulated as: d.sub.1-2 -d.sub.2-3 +d.sub.3-4 -d.sub.4-1 =0 (Eq. 7) which, when not equal to zero, may be regarded as the planarity error EP. If, however, non-planarity is indicated, several possible planes may be considered. For example, as illustrated in FIG. 9C, the non-planarity error may be explained by hinging the surface along the 1-3 diagonal and dividing the surface into two planes, P1 and P2, using displacements d.sub.1-2 and d.sub.2-3 for P1 and d.sub.3-4 and d.sub.4-1 for P2. However, as illustrated in FIG. 9D, the non-planar surface could also be hinged along the 2-4 diagonal, defining P3 using displacements d.sub.2-3 and d.sub.3-4 and P4, using displacements d.sub.4-1 and d.sub.1-2. The above four planes were determined from the four adjacent displacements and may be regarded as forming a tetrahedron as shown in FIG. 9E. Here, planes P1 through P4 form a closed volume. Planes P1 and P2 are hidden from view. The various displacements are also indicated. As indicated by the dimensions relating adjacent and diagonal displacements, it is apparent that in the fourplane tetrahedron shown in FIG. 9E that the sum of the two adjacent displacements equals the actual corresponding diagonal displacements. However, this need not be the case, and as shown in FIG. 9F, when the actual diagonals are considered, each diagonal doubles the number of planes, therefore producing four additional planes with diagonal 1-3 and four additional planes with diagonal 2-4. Thus, twelve possible planes may be found when all six actual displacements are available but only eight may be found when one displacement is missing, as for example, when the correlation quality is too poor to be acceptable. It should be understood that the equivalent virtual displacement may be computed and used in place of the actual diagonal displacement, and still further, pairs of virtual displacements may be used to define the equivalent twelve planes as illustrated in Table I. Where both actual diagonal displacements are available, these may also be used to compute a thirteenth plane. Referring now to Table I, the table illustrates for the previously described cases, how any two related displacements may be combined to produce an equivalent pair of diagonal displacements. Here it is convenient to compute the orthogonal displacements in the illustrated four-pad case along the 1-3 and 2-4 diameters. By related displacements, it is meant that the displacements are related by having one curve in common and for the four-curve tool, since only two related displacements are required which utilize only three of the four curves, one curve may be ignored in each case. Referring to Case 1 of Table I, for example, if the known related displacements correspond to d.sub.4-1 and d.sub.1-2, here related through common curve one, the information obtained from PAD 3 is not required, as indicated by (3) notation in the table. The orthogonal displacements along the 1-3 diagonal and along the 2-4 diagonal may be computed from the relationship indicated in the Table, as was previously described in regard to FIGS. 8C and 8D, respectively. It will be shown that these relationships may also be derived by extending the algebraic subtraction process indicated in FIG. 8A while including the relationships derived from FIGS. 8C and 8D for the virtual displacements. Consider now, for example, Case 6, where no information from Curve 4 is known and only d.sub.2-3 and d.sub.1-3 are to be used. Here, d.sub.1-3 may be used directly for the virtual displacement d.sub.1-3.sup.v indicated in the table, but the virtual displacement corresponding to the diameter 2-4 must be computed from relationships involving only d.sub.2-3 and d.sub.1-3. As an example of the above algebra, consider now how these latter relationships are derived. From FIG. 8A, it can be seen that the difference (d.sub.1-3 -d.sub.2-3) corresponds to d.sub.1-2. Further, from inspection of FIG. 8C, which imposes a condition of planarity and therefore symmetry between opposing displacements, it can be seen that d.sub.3-4 =-d.sub.1-2 and therefore, the relationship needed to compute d.sub.2-4.sup.v from d.sub.2-3 +d.sub.3-4 (Eq. 3A) is completed by substituting -(d.sub.1-2)=-(d.sub.1-3 -d.sub.2-3) for d.sub.3-4 which yields d.sub.2-4.sup.v =d.sub.2-3 -(d.sub.1-3 -d.sub.2-3)=2d.sub.2-3 -d.sub.1-3 as shown in Table II for Case 6. Similar substitutions using the planarity and symmetry assumptions lead to the completion of Table I. It should be noted, however, that different tables would be necessary for dipmeter tools involving different numbers and arrangements of electrodes and corresponding diameter measurements. Recalling that FIGS. 8C and 8D illustrated how orthogonal virtual displacements may be computed in the 1-3 and 2-4 diagonal planes. Then by combining a virtual displacement with the corresponding diameter, a virtual tangent or apparent dip angle in the diagonal plane may be computed using Equations 4 and 5 which correspond to 1-3 and 2-4 diagonal planes. Further, Table I sets forth many additional combinations of related displacements which may be used to derive many sets of pairs of orthogonal displacements, some real, some virtual. When combined with their corresponding diameters as per Equations 4 and 5, these displacements provide a plurality of virtual tangents. Refer now to FIG. 13B, where it will be illustrated how these virtual tangents, computed as above, may be combined to produce an apparent dip .theta.' and corresponding azimuth .phi.' which, as illustrated, are referenced to electrode No. 1 in the electrode plane. When the pair of virtual tangents, which of course are merely orthogonal displacement to diameter ratios, are treated simply as vector distances A and B along a corresponding pair of orthogonal axes, here shown along 1-3 and 2-4 diameters, the derivation of Equations 8 and 9 becomes apparent. The tangent of the dip angle .theta.' is equal to the resultant of the two virtual tangent vectors A and B, and can be found by taking the square root of the sum of the squares of these vectors as illustrated as Equation (8) shown in FIG. 13B. In a more abbreviated form, Eq. (8) may be written as: ##EQU1## where A and B are the results of Equations (4) and (5), respectively, which are also shown in FIGS. 8C and 8D. The apparent azimuth .phi.' is found as the tangent of the angle between this resultant vector and Electrode 1 axis, since this is the standard reference direction. The tangent of this angle, of course, is given by the usual side-opposite over side-adjacent relationship and here corresponds to BA, or when expressed in terms of the virtual tangents, becomes as Equation (9) as shown in FIG. 13B. Note, however, that some consideration for which quadrant the vector falls in must be considered since the azimuth has the possibility of a range from zero to 2.pi. radians (0-360 degrees). Thus, a correction term (K.pi. or K 180.degree.) is added where K corresponds to zero, one, one and two for the first through fourth quadrants, respectively. The tangent of the apparent azimuth .phi.' expressed as radians obtained from Equation (9) may then be converted into degrees if desired. Referring now to FIG. 10A, there is shown a method of treating apparent dip and azimuth values as a vector projected in a unit sphere. The vector is projected from the origin or center of the unit sphere to a point on the surface of the sphere with the tip of the vector defining a point corresponding to each dip termination. Note that the vectors are projected relative to the position of the pads in the electrode plane of the tool. The 1-3 diameters form the X axis, the 2-4 diameters form the Y axis and define an equatorial electrode plane. The axis of the borehole tool forms the Z axis. X and Y are considered positive towards Pads 1 and 2, respectively, Z increases downward along the tool axis. Azimuth values increase in a clockwise direction about the upwards or negative Z tool axis. The position of a vertical line which indicates the topside of the hole is separated from this tool axis by the deviation angle .delta. and from the No. 1 pad axis by the relative bearing .beta., which is not shown in FIG. 10A but is shown in FIG. 2. A given dip and azimuth value may be described in terms of a vector, as shown in FIG. 13B, or as angular relationships in planes parallel to the tool axis and intersecting the orthogonal 1-3 and 2-4 diameters and thus forms a vector which originates at the origin and projects to the three-dimensional surface of the unit sphere. When a number of similar vectors are projected, such as illustrated at G.sub.1 of FIG. 10A, a group or cluster of points would appear on the surface of the sphere. Because the use of such a three-dimensional projection is somewhat inconvenient, it is desirable to transform such projects into two dimensions for most uses. However, it is an important characteristic in the analysis of such groups of vectors to preserve the equal-area statistical attributes of the three-dimensional spherical projection when it is transformed into two dimensions. Expressed in another manner, when a given surface area on the sphere, such as the area dA shown in FIG. 10A is transformed to a two-dimensional area da, the equal-area characteristic should be preserved. This preservation may be obtained by the transformation formula indicated in FIG. 10A which scales the surface of the upper hemisphere, which has a unit radius R, by one-half to correspond to the area of the circle forming the two-dimensional representation. This transformation is such that the radial distance r from the origin to the two-dimensional projection point of the vector for a dip .theta. may be obtained from: ##EQU2## Thus, if each apparent dip angle .theta.' is transformed according to the above transformation, a group of vectors shown as G1 or G2 on the unit sphere would still project as groups G1' or G2' having the same statistical characteristics on the two-dimensional transformation, thus validating any statistical analysis performed on the |