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BACKGROUND OF THE INVENTION  
       [0001]     The present invention is related generally to the field of directional drilling and, more particularly, to electronic roll indexing compensation in a directional drilling system and method.  
         [0002]     Drilling systems generally use a drill string which extends from a drill rig, positioned at the surface of the ground, to an inground boring tool or downhole arrangement which is connected to a foremost end of the drill string. The specific configuration of the downhole arrangement may vary substantially, depending on the specific type of drilling operation that is being performed. Generally, however, directional drilling utilizes some form of downhole assembly which allows for steering the drill head in a controlled manner. In one configuration, the downhole arrangement includes a drill head having an asymmetric face. So long as the drill string is rotated continuously, a straight borehole is formed, assuming uniform soil conditions. In order to steer the drill head, the asymmetric face is oriented in a desired position while the drill string is extended, thereby causing the asymmetric face to produce a lateral force which deviates the borehole. In another configuration, the drill arrangement utilizes a “bent sub” connected to the foremost end of the drill string, which may also be referred to as a “bend sub.” The bent sub is generally attached on one side to the drill string and on the other side to a mud motor which rotates a drill bit which is powered using mud that is pumped down the drill string from the drill rig under considerable pressure. The bent sub provides a slight angular offset of the downhole arrangement with respect to the overall axis of the drill string for purposes of steering. That is, when the bent sub is oriented in a particular direction, using the drill string, for a period of time as the drill string is extended, the angular offset of the bent sub causes the borehole to be deviated in that particular direction. Formation of a straight borehole, using a bent sub, is provided using appropriate rotation of the drill string.  
         [0003]     As is evident from the foregoing discussions, directional drilling requires an awareness of the orientation of the steering mechanism at the inground end of the drill string. In the past, various approaches have been used in order to provide this awareness. With respect to drilling arrangements which utilize an asymmetric drill head, it should be appreciated that a roll orientation signal can be transmitted from a transmitter that is located in the drill head itself, such that the transmitter co-rotates with the drill head. In such an arrangement, simple mechanical expedients may be used such as, for example, indexing tabs so as to index a zero roll position of the transmitter with the asymmetric face of the drill head. In other forms of drilling arrangements such as, for example, those using a bent sub, considerably more complex approaches have been necessary in the prior art to index the transmitter to the steering mechanism, as will be described immediately hereinafter.  
         [0004]     It should be appreciated that a typical bent sub arrangement including a mud motor is generally incapable of carrying a transmitter within the mud motor itself. This result generally obtains since the mud motor is a relatively complex and long assembly having a central rotating drive shaft which rotates the drill bit. A mechanical indexing arrangement for a transmitter is therefore difficult to provide since the transmitter is generally located in the drill string behind the mud motor and the bent sub. Moreover, there will generally be a threaded connection between the drill string, that supports the transmitter, and the bent sub. This threaded connection produces an arbitrary roll orientation therebetween. Accordingly, mechanical indexing arrangements, in the presence of a bent sub or mechanically similar arrangement, tend to be quite complex in order to appropriately index the transmitter zero roll orientation to the steering direction of the bent sub.  
         [0005]     The present invention provides an electronic roll indexing arrangement and method which resolves the foregoing difficulties and concerns while providing still further advantages.  
       SUMMARY OF THE DISCLOSURE  
       [0006]     As will be discussed in more detail hereinafter, there is disclosed herein an apparatus and associated method used in a system for forming a borehole including a drill string which is made up of a series of elongated sections that is connected to a leading arrangement having a steering configuration that is responsive to a roll position thereof, which roll position is controlled using the drill string. In one aspect of the present invention, an assembly is provided that is configured for sensing a roll orientation thereof, referenced to a roll indexing orientation that is defined by the assembly, so as to produce a roll output signal and for transmitting the roll output signal in a predetermined way. A housing is configured to support the assembly in relation to the drill string behind the leading arrangement in fixed rotational communication with the leading arrangement such that the roll indexing orientation is in a fixed, but arbitrary angular offset with respect to the roll position of the leading arrangement. With the assembly supported in the housing, the roll position of the steering configuration is oriented in a predetermined way. The roll output signal is received, with the steering configuration of the leading arrangement oriented in the predetermined way, for use in identifying a value of the fixed angular offset. The value of the fixed angular offset can then be saved.  
         [0007]     In another aspect of the present invention, in which an apparatus and associated method are used in a system for forming a borehole including a drill string which is made up of a series of elongated sections that is connected to a leading arrangement having a steering configuration that is responsive to a roll position thereof, which roll position is controlled using the drill string, an assembly is configured for sensing a roll orientation thereof, referenced to a roll indexing orientation that is defined by the assembly, so as to produce a roll output signal and for transmitting the roll ouput signal in a predetermined way. A housing is configured to support the assembly for fixedly co-rotating the assembly with the leading arrangement such that the roll indexing orientation is in a fixed angular offset with respect to any given roll position of the leading arrangement, which fixed angular offset is arbitrarily established between the housing and the leading arrangement. A roll compensation value is established that is a constant in view of the fixed angular offset. The roll compensation value can then be saved. 
     
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0008]     The present invention may be understood by reference to the following detailed description taken in conjunction with the drawings briefly described below.  
         [0009]      FIG. 1  is a diagrammatic view, in elevation, of one embodiment of a downhole arrangement that is produced in accordance with the present invention.  
         [0010]      FIG. 2  is a diagrammatic view of an orientation system in a clock face format, shown here to illustrate an angular positional relationship between a roll orientation of the steering configuration and the transmitter initially shown in  FIG. 1 .  
         [0011]      FIG. 3  is a diagrammatic elevational view of one embodiment of a housing having a transmitter supported therein according to the present invention, wherein the housing walls are shown as being transparent for illustrative purposes.  
         [0012]      FIG. 4  is a diagrammatic view, in cross-section, of the housing of  FIG. 3 , shown here to illustrate further details with respect to its construction and the transmitter therein.  
         [0013]      FIG. 5  is a diagrammatic end view of one end of the housing of  FIGS. 3 and 4 , shown here to illustrate further details with respect to its structure.  
         [0014]      FIG. 6  is a partially cut-away diagrammatic cross-sectional view of one end of the housing of  FIGS. 3-5 , shown here to illustrate details with respect to a first plug that engages one end of the housing and the transmitter supported therein.  
         [0015]      FIG. 7  is a diagrammatic cross-sectional view of a second plug that engages the other end of the housing and the transmitter therein including an angular indexing arrangement which fixes the angular orientation of the transmitter with respect to the housing.  
         [0016]      FIG. 8  is a diagrammatic view, in perspective, of the second plug of  FIG. 7 , shown here to illustrate further details with respect to the angular indexing arrangement.  
         [0017]      FIGS. 9-12  are flow diagrams which cooperatively illustrate the present invention.  
         [0018]      FIGS. 13   a - d  are diagrammatic illustrations of a display screen which may form part of a portable device, shown here to illustrate its operation and the display of roll parameters with respect to the display and selection of unmodified and modified roll display modes. 
     
    
     DETAILED DESCRIPTION  
       [0019]     Turning now to the figures, in which like reference numbers are used to refer to like items whenever possible throughout the various figures, attention is immediately directed to  FIG. 1  which illustrates a downhole drilling arrangement produced in accordance with the present invention and generally indicated by the reference numeral  10 . It is noted that the figures are diagrammatic for purposes of enhancing the reader&#39;s understanding. Further, the drawings are not to scale for purposes of better illustrating features that are of interest. Moreover, terminology such as, for example, behind/ahead, vertical/horizontal, left/right and up/down is used for descriptive purposes only and is in no way intended as being limiting.  
         [0020]     Still referring to  FIG. 1 , arrangement  10  includes a drill bit  12  which is rotated, for example, by a mud motor (not shown) contained by a mud motor section  16 . It is noted that such mud motors are well-known to those having ordinary skill in the art. The mud motor is often hydraulically operated using drilling mud that is pumped down a drill string  20  (only partially shown) in a direction indicated by an arrow  22  from a drill rig (not shown) operating at the surface of the ground. The drill string is typically assembled in sections as drilling progresses, using mated drill pipe sections having what are commonly referred to as threaded “box” and “pin” connections. A leading end of the drill string supports a transmitter housing  26  which is configured for containing a transmitter  28  therein, as will be described in further detail hereinafter.  
         [0021]     A bent sub  34  is used to connect transmitter housing  26  to mud motor section  16  in order to provide a slight lateral angular offset with respect to the overall drill string for steering purposes, as is described above. It is noted that the lateral angular offset has been exaggerated in the present figure for illustrative purposes. The lateral angular offset provides for steering the drilling operation by orienting the drill bit, responsive to the lateral angular offset, to proceed in a desired direction. Unfortunately, a box and pin fitting set  36  is introduced between transmitter housing  26  and mud motor  16 . Box and pin fitting set  36  presents a problem with respect to the fact that this fitting arrangement will not seat in a predictable angular orientation, such that, for any given rotational orientation of transmitter  28 , the roll orientation of bent sub  34  is arbitrary, as will be further described immediately hereinafter.  
         [0022]     Referring to  FIG. 2 , a diagrammatic end view illustrates a clock face  60  in which the bent sub is oriented at 12 o&#39;clock as indicated by an arrow  62 . An arrow  64  illustrates an arbitrary orientation of a reference or indexing orientation of the transmitter such that an angle α represents an angular offset between the orientation of the bent sub and the reference or indexing orientation of the transmitter. The transmitter indexing orientation represents a roll orientation of the transmitter at which it outputs a zero roll value. Thus, in the present example, the transmitter will indicate a roll orientation of approximately 4 o&#39;clock, even though the bent sub steering direction is at 12 o&#39;clock.  
         [0023]      FIG. 1 , likewise illustrates the bent sub in a 12 o&#39;clock orientation. In this regard, it is noted that any suitable nomenclature may be used for characterizing angular orientation including the use of degrees, measured from any suitable reference. As described above, maintaining any given orientation of the bent sub over time during drilling causes a deviation of the borehole in the direction of the given orientation. Rotation of the drill string in a continuous manner, indicated by an arrow  66 , results in the formation of a generally straight borehole, at least in the presence of homogeneous soil conditions. Accordingly, it is important for an operator to be aware of the roll orientation with respect to steering. It is to be understood, however, that the present invention is not limited to use with bent sub type downhole assemblies and may be used in any situation where there is a need to correlate the roll position of a leading portion of the downhole assembly with the roll orientation of a transmitter that is spaced away or separated from the leading portion in a way which may introduce an angular roll offset of an arbitrary, but constant nature between the leading portion of the downhole assembly and the transmitter. Moreover, complex mechanical indexing configurations, for referencing the transmitter roll, for example, to a sloped drill face, may be eliminated in favor of the approach of the present invention.  
         [0024]     Again directing attention to transmitter  28 , this transmitter may be configured in one form for emanating an electromagnetic field  70  such as, for example, a dipole field. Various information may be impressed upon the electromagnetic field or such information may be carried to an aboveground location in other suitable ways. Digital and/or analog information can be modulated on the electromagnetic field or the field may be switched on and off appropriately to transmit the desired information. Information can be transmitted up the drill string, for example, using mud pulsing or using wire-in-pipe arrangements for sending electrical signals (analog and/or digital) up the drill string to the drill rig for use aboveground. While the information of interest can include different types of orientation information, as well as information relating to the operation of the transmitter such as, for example, temperature and battery condition, the specific operational parameter that is of interest here is the roll orientation of the transmitter.  
         [0025]     In the instance of transmitting digitally encoded roll information, any suitable programmable receiver may be used to receive the information. One example of such a receiver, in the form of a portable walkover detector, is given in U.S. Pat. No. 6,496,008 (hereinafter the &#39;008 patent) which is commonly owned with the present application and is incorporated herein by reference. FIG. 1 of the &#39;008 patent illustrates a programmable receiver which may receive and decode roll orientation information. Of course, a receiver may be positioned at the drill rig having a connection to a wire-in-pipe arrangement, or mud pulsing arrangement, such that the roll orientation information is transferred up the drill string for use at the drill rig. Alternatively, the roll orientation information can be telemetered from the drill rig for display or use at other locations. Useful wire-in-pipe arrangements are described in U.S. Pat. Nos. 6,223,826, 6,446,728 and 6,655,464, all of which are commonly owned with the present application and incorporated herein by reference.  
         [0026]     Referring now to  FIG. 3 , details will now be provided with respect to one configuration of transmitter housing  26 . The latter includes a housing or shell  80  which may be formed from suitable materials such as, for example, ANSI 4140, Monel K500. Housing  80  is illustrated as being transparent for illustrative purposes in a diagrammatic side view to show three slots  82 a-c that may be defined therein for purposes of emanating an electromagnetic signal (see  FIG. 1 ) from transmitter  28 , in the instance where such a signal is used. At least an outer portion of each slot is sealed with a suitable material (not shown) that allows transmission of the electromagnetic field therethrough. Such sealing materials include, for example, epoxy. It is understood that the use of three equi-angularly distributed slots represents only one of a number of possible slot configurations which may be defined by the housing. The housing further defines first and second opposing box fittings  84  and  86 , respectively, for engaging the drill string and bend sub, respectively (see  FIG. 1 ). It should be appreciated that box fittings  84  and  86  may be of different configurations, as illustrated, to accommodate pin fittings of any particular drill string and/or bent sub. It is noted that box fitting  86  forms part of fitting set  36  of  FIG. 1 .  
         [0027]     Referring to  FIG. 4  in conjunction with  FIG. 3 , the former is a diagrammatic cross-sectional view taken generally along a line  4 - 4  in  FIG. 3 . Housing  80  defines a plurality of mud passages  90   a - c , equi-angularly distributed about an elongation axis of housing  80  for use in transferring drilling mud from the drill string to the mud motor or drill bit. As seen in the view of  FIG. 4 , with respect to slot  82   b  and mud passage  90   b , each mud passage is arranged opposite each slot with respect to the elongation axis of the housing.  
         [0028]     Referring to  FIGS. 4 and 5 , the latter provides a diagrammatic end view of housing  80  looking at box fitting  86  to further illustrate the relationship between slots  82  and mud passages  90 . Mud passages  90  lead into each of the box fittings at either end of housing  80 . It is noted that box fitting  86  includes an enlarged annular mud receiving region  100  (see  FIGS. 3 and 4 ) as a result of the relatively reduced diameter of box fitting  86  for attachment to the bend sub.  
         [0029]     Referring to  FIGS. 3 and 4 , a transmitter receiving passage  110  is axially centered within shell  84  for receiving transmitter  28 . Opposing entrance openings of passage  110  include an inside thread  112  to engage first and second threaded plugs  114  and  116 , respectively, as will be further described immediately hereinafter.  
         [0030]     Referring to  FIGS. 3, 4 , and  6 , with transmitter  28  in its installed configuration within housing  80 , end plug  114  threadingly engages passage  110  in a way which captures a helical coil biasing spring  120  between transmitter  28  and end plug  114 .  FIG. 6  is a cross-sectional view of end plug  114  which illustrates a through passage  124  defined therein. This through passage can be provided for accommodating an electrical conductor  126  (see  FIGS. 3 and 4 ) for connection to a wire-in-pipe arrangement. Wire  126  may be sealed against the interior of passage  124  in any suitable manner such as, for example, using a plug (not shown) with an  0 -ring to form a compression seal around the insulation of the electrical wire. Of course, through passage  124  may be eliminated in the instance of transmitting the roll and other information using an electromagnetic signal. Likewise, where a wire-in-pipe transmission arrangement is used, slots  82  may be eliminated. Plug  114 , like plug  116 , includes a hex head  128  for use in installing each of the plugs, although any suitable configuration can be used for this purpose. An O-ring  130  is received in an O-ring groove  132  that is defined by the plug body. O-ring  130  sealingly engages an interior sidewall of passage  110  peripheral to the entrance into the passage at either end from box fittings  84  and  86 .  
         [0031]     Turning to  FIG. 7  and  8  in conjunction with  FIGS. 3 and 4 , plug  116  will now be described in further detail.  FIG. 7  provides an enlarged cross-sectional view of plug  116  installed within passage  110  and positioned against one end of transmitter  28 .  FIG. 8  illustrates plug  116  in relation to a corresponding end of transmitter  28  in an enlarged perspective view. As seen through the combination of  FIGS. 4 and 8 , plug  116 , like plug  114 , includes an outer thread  150  for engaging inner thread  112  of passage  110  in housing  80 .  FIGS. 7 and 8  further illustrate an alignment tab  152  which extends outwardly from the body of plug  116 . Alignment tab  152  is configured to engage a slot  154  which is defined by an end cap  156  of transmitter  28 . Generally, alignment slot  154  defines the reference indexing and zero roll orientation of the transmitter. End cap  156  is installed in the elongated body of transmitter  28 , at least in part, using capture fingers  158  that are seen in  FIGS. 4 and 7 . Installation of transmitter  28  within housing  80  can be accomplished by first installing plug  114  and biasing spring  120  within housing  80 . Transmitter  28  is then slidingly received in passage  110  to engage biasing spring  120 . Thereafter, end plug  116  is installed in the opposing end of passage  110 . As end plug  116  is rotated, alignment tab  152  is received within slot  154  of the transmitter to, thereafter, co-rotate with the end plug. Plug  116  is then seated against housing  80  at box end  86  so as to effectively “lock” the transmitter in position rotationally with respect to housing  80 . Accordingly, transmitter  28  is resiliently captured between spring  120  and end plug  116  in a fixed rotational orientation which itself is arbitrary with respect to the housing. What is important, however, is that this orientation, even though arbitrary, is fixed and will not vary when the housing and transmitter therein are exposed to potential underground conditions. In this regard, it should be appreciated that the relationship between the housing and the mud motor, shown in  FIG. 1 , is also fixed, but arbitrary. Accordingly, the overall relationship between the transmitter and the steering direction of the mud motor is fixed, but arbitrary. Again, the arbitrary nature of the overall relationship between the transmitter and the steering configuration that is used is not a concern so long as the relationship remains fixed after it is initially established. With brief reference to  FIG. 8 , it is noted that a circular marking  170  is present at the end of the transmitter adjacent to slot  154 . This marking is color-coded and represents an option that is used for purposes of indicating the temperature tolerance of transmitter  28 .  
         [0032]     Having described in detail above the physical attributes of the present invention, attention is now directed to its accompanying method. Specifically,  FIG. 9  is a flow diagram, generally indicated by the reference number  200  which illustrates a setup mode, forming at least a portion of the method of the present invention, which can be performed using any suitable receiver that is capable of receiving the roll output signal transmitted from transmitter  28 , as described above. Such a receiver generally includes a display such as, for example, an LED, LCD, and/or plasma display for presenting information of interest to an operator of the receiver. The receiver usually comprises a portable device such as described, for example, that may be provided on a portable device such as, for example, on the walkover locater that is illustrated in the above incorporated &#39;008 patent. Alternatively, the roll output signal may be received at the drill rig and displayed there and/or a telemetry system may transmit the roll output signal, or related data, to another aboveground location.  
         [0033]     Continuing with a description of flow diagram  200 , the setup mode is entered at step  202  and proceeds to step  204 . In step  204 , the receiver provides an option to the operator for entering the setup mode. If the operator elects not to do so, the system reverts to the normal operation mode in step  206 . If, however, the operator elects to set the roll offset, step  208  prompts the operator with the option to enter a manual setup mode. If the operator chooses to enter the manual setup mode, execution moves to step  210 , thereby initiating the manual setup mode. This mode will be described with reference to a subsequent flow diagram. Where the operator in step  208  elects not to enter the manual mode, operation continues to step  212  which prompts the operator to place the steering configuration into a target roll position. The latter may be any position which is convenient, however, in most instances it should be convenient to orient the steering configuration such as, for example, a bent sub in an upward orientation (i.e., 12 o&#39;clock). With collective reference to  FIG. 1 , it is noted that this step may be performed so long as at least transmitter  28 , housing  26  and bent sub  34  are assembled so as to fix their rotational orientations with respect to one another, although the specific final orientation can be arbitrary. Subsequent connection of mud motor  16  should not affect this fixed rotational orientation, as is likewise the case with respect to attaching drill string  20  to housing  26 . Thus, flexibility is provided with respect to the assembly state of the downhole arrangement when this setup is performed.  
         [0034]     Having prompted the operator to place the steering configuration into the target roll position, step  214  then queries the operator to ascertain whether the steering configuration is in the target roll position. If not, a loop including steps  212  and  214  is entered until the condition is satisfied. Once it is confirmed by the operator that the steering configuration is in the target roll position, step  216  reads a current roll output based on a current value of the roll output signal from transmitter  28 . The current roll output signal is then used in step  218  to determine the offset angle a and this value is saved for future reference. Step  220  then sets a roll offset flag so as to indicate that the system is in an operating mode which invokes the use of the roll offset value whenever a roll position of the steering configuration is to be determined. Normal operation then resumes in step  206 . It is noted that the roll offset may be set and cleared in any suitable manner. As one example, a single digital bit may be used wherein a set state is represented by a one while a cleared state can be represented by a zero. Of course, negative logic may be employed wherein these states, with respect to the bit, are reversed.  
         [0035]     Turning now to  FIG. 10 , attention is now directed to a portion of the normal operation mode which forms part of the method of the present invention. It is noted that the sequence illustrated is only part of an overall normal operational mode that is of specific interest here. Illustration of the complete overall normal operational mode is beyond the scope of the present discussion since the “sub-process” under discussion may be implemented in any number of different ways and placed at different positions in the context of the overall normal operational mode. This figure comprises a flow diagram that is generally indicated by the reference number  300  and begins at step  302  within the overall normal operational mode. Step  304  then tests the roll offset flag. When the roll offset flag is cleared, operation proceeds to step  306  which causes the display of an unmodified roll orientation. Optionally, an indication may be provided to the operator that the regular or unmodified roll value is in use. This may be referred to, for example, as the “regular roll mode.” In essence, the roll orientation of transmitter  28  is displayed. At step  308 , the normal operational mode then resumes. Returning to step  304 , in the instance when the roll offset flag is set, step  310  then uses the saved roll offset value to determine a current modified roll value in conjunction with a current value of the roll output signal being transmitted by transmitter  28 . Step  312  then displays the current modified roll value and, optionally, may provide an indication to the operator that the modified roll indication system is in use. This may be referred to, for example, as the “modified roll mode.” Thereafter, step  314  provides an opportunity to the operator to alter the current roll offset value that has been saved. If the prompt is answered in the negative, the normal operation mode resumes at step  308 . If, on the other hand, the operator elects to alter the roll offset value, step  316  saves a new roll offset value based on the current roll output signal of transmitter  28 . That is, the current roll position of the steering configuration, depending upon the specific nomenclature in use for describing the roll orientation, will become the “home”, reference, zero roll position or 12 o&#39;clock position, whenever the modified roll mode is invoked, irrespective of the actual roll position of the steering configuration. The opportunity to alter or adjust the roll offset value is convenient for purposes of providing minor adjustments in order to fine-tune steering or to correct steering bias due to a specific design of the drill bit.  
         [0036]     Turning now to  FIG. 11 , a flow diagram, generally indicated by the reference number  320 , illustrates the aforementioned manual roll offset setup mode. This mode is initiated at step  322  and proceeds to step  324  in which the operator is queried for entering a manual roll offset value. If the operator elects not to enter a roll offset value step  326  then determines whether the operator would like to clear the offset value and thereby enter the regular roll mode. If the operator elects not to clear the offset value, step  328  returns the system to normal operation in the modified roll mode. If the operator elects to clear the offset value, step  330  clears the roll offset flag such that normal operation resumes in the regular roll mode. Returning to step  324 , if the operator elects to manually enter a roll offset value, step  332  provides a prompt to enter this value. Step  334  reads and saves the operator entered roll value and step  336  then sets the roll offset flag. Normal operation then resumes in step  328  using the modified roll mode.  
         [0037]      FIG. 12  illustrates a portion of the normal overall operational mode, generally indicated by the reference number  350 , for selectively canceling the modified roll mode to thereafter proceed in the regular roll mode. From some suitable point in normal operation, indicated by step  352 , execution is passed to step  354  wherein a query determines whether it is desired to cancel the use of the roll offset value, that is, to revert from the modified roll mode to the regular roll mode. If this query is answered in the negative, the modified roll value is displayed thereafter, as required by step  356 , when the normal operational mode resumes in step  358 . On the other hand, when the query of step  354  is answered in the affirmative, step  360  clears the roll offset flag. Step  362  requires display thereafter of the unmodified roll value. Again, the overall procedure embodied by the flow diagram presently under discussion may be invoked at any suitable point or points within the normal operational mode of the receiver.  
         [0038]      FIGS. 13   a - d  are screen shots which illustrate a display, generally indicated by the reference number  400 , that may be provided on a portable device such as, for example, the walkover locater that is illustrated in the above incorporated &#39;008 patent. Each figure includes a centered illustration  402  of the locator that is in use in relation to a field defined point  404  which is established in some way through using a particular form of locating signal such as, for example, a dipole field. Each of the subject figures further illustrates a drill head pitch  406  using an appropriate symbol, below which appears a current pitch measurement  408 . In the present example, the latter is shown as 2.8% and is indicated as being upward by symbol  406 . A signal strength indication  410  is indicated in one corner of display  400 . In the present example, the indicated signal strength is “523”. The upper right hand corner of display  400  includes a roll indicator  420  in the form of a clock face. It is noted that these various display elements may be reorganized in any appropriate manner or combination, based on a particular application, and the present figures are in no way intended as being limiting.  
         [0039]     Referring specifically to  FIG. 13   a , a query  422  is being presented to the operator requesting confirmation of an initial request to set a new roll offset. The operator may set a new roll offset by selecting “Y” for yes or may cancel by selecting “N” for no. It is noted that roll indicator  420  is illustrating an actual or uncompensated roll value of 4 o&#39;clock. Of course, if the operator selects “N”, the appearance of roll indicator  420  will be unchanged.  
         [0040]      FIG. 13   b  illustrates the appearance of display  400  when “Y” is selected in the display of  FIG. 13   a . Specifically, roll indicator  420  illustrates a modified roll of 12 o&#39;clock. Display  400  then provides a roll offset notification  426  which indicates that modified roll is in use and that the offset value is 240 degrees, measured clockwise from 12 o&#39;clock. Notification  426  serves to continually remind an operator that roll offset is currently in use, although such notification could be provided intermittently and is not a requirement.  
         [0041]      FIG. 13   c  illustrates the appearance of display  400  including a query  430  which is presented to the operator. If the operator, selects “N” (for “No”), the query disappears and the roll offset will remain at 240 degrees such that roll indicator  420  shows the modified roll orientation value.  
         [0042]      FIG. 13   d  illustrates the appearance of display  400  still including query  430 . If the operator selects “Y” (for “Yes”, roll offset ends and notification  426  disappears along with query  430 .  
         [0043]     Having described the present invention in detail above, it is worthwhile to note that the described approach is considered to provide an elegant, highly practical and reliable solution to the problem of roll orientation indexing, as discussed above with respect to the prior art. In particular, the need for a mechanically complex and generally expensive mechanical roll indexing arrangement is eliminated.  
         [0044]     It is noted that portions of the descriptions herein are presented in terms of symbolic representations of operations on data bits within an electronic device. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. The operations are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities.  
         [0045]     Although each of the aforedescribed physical embodiments have been illustrated with various components having particular respective orientations, it should be understood that the present invention may take on a variety of specific configurations with the various components being located in a wide variety of positions and mutual orientations. Furthermore, the method described herein may be modified in an unlimited number of ways, for example, by reordering, modifying and recombining the various steps. Accordingly, it should be apparent that the arrangements and associated method disclosed herein may be provided in a variety of different configurations and modified in an unlimited number of different ways, and that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and methods are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified at least within the scope of the appended claims.

Summary:
An assembly is configured for sensing its roll orientation, referenced to a roll indexing orientation that is defined by the assembly, so as to produce a roll output signal and for transmitting the roll output signal in a predetermined way. A housing is configured to support the assembly for fixedly co-rotating the assembly with the leading arrangement such that the roll indexing orientation is in a fixed angular offset with respect to any given roll position of the leading arrangement, which fixed angular offset is arbitrarily established between the housing and the leading arrangement. A roll compensation value is established that is a constant in view of the fixed angular offset. In one feature, the roll output signal is received with the steering configuration of the leading arrangement oriented in a particular way, for identifying a corresponding value of the fixed angular offset.