Abstract:
An attachment to a standard measuring rule includes a body securely supporting the measuring rule. Within the body a vernier is provided. The vernier divides twenty-four one-eighth inch divisions into twenty-five equal parts, enabling vernier measurements in units of five-thousandths of an inch. A second vernier with marks spaced by one thousandth of a unit less than said measuring rule enables resolution to thousandth units. The results of the first and second verniers can be summed to yield non-interpolated resolution in thousandths of an inch from a fractional rule. Replacement rules and verniers further enable the measuring instrument to alternatively measure tolerance limits, providing the measuring instrument the adaptability to be converted readily into an easy to read quality control instrument.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 09/259,895, filed Feb. 27, 1999 now U.S. Pat. No. 6,205,673 issued on Mar. 27, 2001, the contents which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to geometrical instruments, and more specifically to straight-edge rules that include an index for subdividing the scale, commonly referred to as a vernier. 
     2. Description of the Related Art 
     Devices for measuring distances and geometries of objects are quite old, dating back to prehistoric times. The early devices were designed to measure using units associated with commonly available objects, such as forearms, hands and feet. Distances were generally defined in whole units and fractions were used only infrequently, being more difficult to calculate and determine. Commonly available objects were identified that could be used for smaller and larger measurements, which reduced the need for fractions or large values. Eventually, whole unit measurements gave way to fractional divisions of existing units, such as the division of one foot into twelve equal inches. Inches were further divided into fractions by halves, into one-half inch, one-quarter inch, one-eighth inch and smaller divisions. For the purposes of this disclosure, fractional units are defined as this division of whole units by multiples of two, and will be specifically understood to include these units of half, quarter, eighth, and so forth. 
     As time has passed from those early days, so has the development of technology. Advances in technology requiring smaller, more durable, longer life devices have been accepted as commonplace, yet the foundation required for these advances is often misunderstood or taken for granted. 
     To manufacture smaller components, components at greater yield and lower prices, or components capable of special performance or reliability requires the ability to introduce precision into the tools, machines and processes that are used to produce the resulting components. These tools, machines and processes must have the same or better precision than that of the finished component. Yet, determining the precision of the tools, machines and processes requires the use of measuring devices capable of measuring widely diverse devices and objects. The measuring devices must, once again, have precision equal or greater than the precision required of the tools. The precision must start with the instruments used to measure other devices and objects. 
     In modern production, these measurements are often more precise than would be readily identified by fractions of an inch, even though many measurements are still specified based upon the fractional system. For example, a hole might be identified as having a one-half inch diameter, but precision may be specified to the nearest hundredth of an inch. Another dimension may be specified as having an outside diameter of 0.625 inches, which is five-eighths of an inch, with a tolerance of plus or minus five thousandths of an inch. These types of mixed fractional and decimal dimensions are commonplace in a manufacturing environment today. 
     Unfortunately, the development of instruments that readily measure and evaluate these fractional and decimal dimensions has not kept pace with the changing needs of the manufacturing environment. Calculators have been developed that will perform conversions between decimal and fractional formats. However, these calculators are not well suited to a manufacturing environment, and are prone to being destroyed by contamination, spills or accidental impact with tools, equipment or the shop floor. They must also be carried about to be of any real use on the shop floor, therefore requiring yet another pocket or pouch. Furthermore, the use of a separate device from the measuring instrument requires a separate step of keying information into the calculator, taking valuable time and introducing the possibility of keying errors. Since there is no direct visual feedback of proportions or relationships between the units of measure, these mistakes may easily go unnoticed until a later time, when the cost of the error is amplified by production of many bad parts. 
     In the prior art, measuring devices frequently have fairly well developed attachments which allow the measurement of a wide and diverse set of components. Typically, these measurements will include inside and outside diameters, elevations, thickness, gap and other similar measurements. Unfortunately, and in spite of their flexibility at measuring diverse components, these instruments are calibrated to either fractional or decimal measuring, but do not provide the ready ability to convert from one format to another. 
     U.S. Pat. No. 897,437 to Watson is representative of early versions of measuring instruments having both coarse and fine measurement which are capable of measuring a variety of dimensions. A straight rule is provided that has standard graduations marked thereon. Onto the rule there are clamped several arms which extend perpendicularly from the rule. These arms enable the measurement of diverse dimensions by allowing a part to be placed between the arms, to measure thickness or outside diameter, or allowing the arms to be placed within the part, such as for inside diameter. While these types of instruments have met with great success in the trade because of their tremendous versatility in taking measurements of many different types, several deficiencies are noteworthy. In particular, one or both of the adjustable arms cover a large number of graduations on the rule. Since most rules use larger and smaller marks to distinguish different graduations, covering up adjacent marks makes it much more difficult to discern quickly and accurately the particular graduation that is exposed. In addition, the precision of these devices is limited to the smaller sizes of graduations that may be placed upon the scale. While in theory a very large number of such graduations are possible, attempting to place them on the scale and still remain legible and useful is not practically possible. In practice, even scales divided to a sixteenth of an inch become visually “busy”, and these finer scales require more time to accurately discern the measurement. 
     A second limitation is in the ability to quickly convert from fractions to decimals, such as when the part is specified by a combination of fractional and decimal units. 
     A third limitation arises from the fact that the alignment for measuring must occur between two perpendicular planes. The vertical edge of a movable body must be visually aligned with a horizontal graduation mark. Because the vertical edge and horizontal mark are not co-planar, and are furthermore not of similar width and dimension, accurate correlation between the two different structures is difficult. As a result, any precision beyond the usual sixteenth of an inch is increasingly difficult. 
     In order to overcome the human visual limitation of reading closely spaced graduations, vernier scales were developed such as disclosed by Homan in U.S. Pat. No. 1,602,490; Berger in U.S. Pat. No. 1,888,305; and Huffman in U.S. Pat. No. 1,888,597. The graduations on the vernier align with the main scale only at the appropriate fractional point of measurement. For example, in the decimal system of measurement, a vernier will divide into ten equal spaces the distance occupied by nine spaces on the scale. When the first vernier graduation mark aligns with a graduation mark on the main decimal scale, the vernier will indicate one-tenth the smallest main scale division. So, carrying this example further, if the main scale is divided into tenths of an inch, the vernier will be calibrated to identify hundredths of an inch without visually cluttering the main scale. This concept has also been widely adapted into the measuring instruments of the prior art, since they quickly advanced the resolution of these versatile instruments. 
     Alternatives to the vernier have been proposed, such as the sawtooth line of Clay in U.S. Pat. No. 4,607,436. However, these alternatives have not proven to offer sufficient benefit in reading the scale with precision for most applications. Furthermore, these scales are more difficult to produce with the intended accuracy. 
     There is a definite need to convert readily between fractional and decimal units, without the need for resorting to special calculators or extremely expensive and complicated devices. This need has not been fully realized by existing instruments. 
     SUMMARY OF THE INVENTION 
     In a first manifestation, the invention is an instrument for measuring distances. A rule is provided having primary fractional graduations and secondary graduations. An adjustable body which is movable with respect to the rule has vernier index graduations adjacent to the rule&#39;s fractional graduations for subdividing the rule. Alignment of one vernier index graduation with an adjacent rule fractional graduation designates a decimal division of the rule&#39;s fractional graduation into precise five-thousandths of a unit. Alignment of the second vernier index graduation with an adjacent rule fractional graduation designates a decimal division of the rule&#39;s fractional graduation into precise thousandths of a unit. 
     In a second manifestation, the invention is a method of measuring a first distance between a first point and a second point with a fractionally graduated rule and converting the distance measurement into a decimal distance measurement. The method comprises the steps of: determining an approximate measurement of the first distance; aligning a reference on a first movable member with a first whole unit graduation mark; spacing a reference on a second movable member from the first movable member reference by a precise distance standard; engaging the first point with the second movable reference; moving the first movable member reference relative to the rule to engage the second point with the first movable member; evaluating a first vernier to convert a first fractional distance to decimal distance with a resolution without interpolation of five-thousandths of a unit; evaluating a second vernier to convert a second fractional distance to decimal distance with a resolution without interpolation of one-thousandths of a unit; evaluating the rule and second movable member to determine a fractional distance between the first and second points in decimal form, with a resolution of one-eighth unit; and summing fractional distance, five-thousandths decimal distance, and one-thousandths decimal distance to yield a total decimal distance between first and second points in decimal form with a resolution of one-thousandth unit. 
     In a third manifestation, the invention is a tolerance gauge for determining whether a desired distance between a first point and a second point in a first direction defining a distance axis on a precision-machined component is within a predetermined maximum distance and a predetermined minimum distance. A rule extends longitudinally in a second direction which defines a rule axis and has at least one graduation thereon representative of the desired distance. A first member is fixed with respect to the rule for accurately locating the rule with respect to the first point. A second member accurately locates the second point relative to the rule by movement of the second member relative to the rule along the rule axis. First and second graduations, each fixed with respect to the second member, represent the predetermined maximum distance and predetermined minimum distance. The first and second graduations are oriented to align with the rule graduation at the predetermined maximum distance and predetermined minimum distance, respectively. 
     OBJECTS OF THE INVENTION 
     A first object of the invention is to provide a vernier for use with a common fractional rule which converts the fractional rule into decimal measurements. A further object of the invention is to provide decimal precision in thousandths of an inch from an eighth-inch rule scale. Another object of the invention is to provide the vernier as part of an assembly which adapts a standard rule to the measuring of many diverse dimensions. Yet another object of the invention is the provision of a vernier on the same plane as the rule graduations, which further only minimally or more preferably does not at all block the adjacent rule graduations. Another object of the invention is the provision of both fractional and decimal verniers on the same device, most preferably both co-planar with the standard rule. These and other objects of the invention are accomplished in the preferred and alternative embodiments, which will be best understood when considered with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a first embodiment of the invention by exploded assembly view. 
     FIG. 2 illustrates a second embodiment of the invention by top plan view. 
     FIG. 3 illustrates a third embodiment of the invention by top plan view. 
     FIG. 4 a  illustrates the exact alignment of a set of graduations of the first three embodiments, while FIG. 4 b  illustrates interpolation which results from equidistant spacing between two adjacent graduations. 
     FIG. 5 illustrates a preferred method for conversion of fractional measurements to decimal values in accord with the present invention. 
     FIG. 6 illustrates a fourth embodiment of the invention by top plan view. 
     FIG. 7 illustrates a fifth embodiment of the invention by top plan view. 
     FIG. 8 illustrates an alternative method for conversion of fractional measurements to decimal values in accord with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a first embodiment of the invention which incorporates the teachings of the invention into a compact, portable, rugged and versatile instrument  100  which finds utility in measuring a variety of dimensions. Instrument  100  has a base  110  which acts as a primary substrate about which other components may be assembled. Within base  110  is a longitudinal groove  120  having slightly elevated edges  121 ,  122 . Groove  120  with edges  121 ,  122  acts as a receiver into which a standard rule  160  may be placed. The actual length of rule  160  is irrelevant to the invention, though a typical one-foot rule is shown in this illustration. By providing slight edges  121  and  122  within groove  120 , rule  160  will be more securely held with less tendency towards wobble, in the event either rule  160  or base  110  are not perfectly planar. Base  110  additionally has a hole  123  extending transverse through body  120 , and hole  123  passes through a perpendicular opening  124 . Into hole  123  may be inserted a hand or thumb screw  130  having a small head  132  and threads  134 . Into hole  124  a generally cylindrical rod  140  may be inserted. Rod  140  has a threaded hole  142  therein which is designed to mate with threads  134 . In view of the cylindrical nature of hole  124  and rod  140 , rod  140  will not be able to spin in the direction of thread rotation. Therefore, when thumb screw  130  is rotated, rod  140  will be drawn by threads  134  towards head  132 . With rule  160  placed within groove  120 , the small elevated region  144  of rod  140  will be drawn against edge  164  of rule  160 , which will in turn push rule  160  towards vernier  152 . Most preferably, vernier  152  will be slightly elevated at ends  150 , 154  thereon, ensuring a two point contact between vernier  152  and edge  162 . By so designing the interface between rule  160  and body  120 , several advantages may be attained. First, a three-point anchor is provided at region  144  and ends  150  and  154  which is very secure and free from wobbling which would otherwise make precise and repeatable measurements difficult or impossible. Second, surface graduation marks upon rule  160  are co-planar with surface graduation marks on body  110 , making the comparison of marks much easier than was known in the prior art. Since graduation marks may be typically depressed slightly into the surface or alternatively raised therefrom, light reflecting from the differences in graduation mark elevation may be reflected and optically determined from rule to vernier, allowing a person to more easily visually determine alignment of marks to great precision. 
     Body  110  may further include various surfaces useful in measuring special dimensions or shapes, such as inside diameter or height measuring lip  125 , arms such as arms  127  and  128 , and an outside diameter or thickness or height measuring face  126 . In addition, as shown in this embodiment, several different verniers  152  and  156  may be provided adjacent on opposite edges of rule  160 , so that measurements may be taken in the standard fractional scale through vernier  156 , or through the decimal vernier  152  which will be described in greater detail hereinbelow. 
     A cover  170  is preferably provided which serves as a fourth enclosing surface to help retain and guide rule  160  within groove  120 . Cover  170  has holes  172  formed therein through which threaded or other fasteners may pass, preferably extending into threaded holes  129  within body  110 . Cover  170  may take a variety of shapes, but most preferably the “L” shape illustrated in FIG. 1 offers significantly improved visibility to each of the verniers  152 ,  156 . Cover  170  will not block graduation marks which may be needed to quickly ascertain a measurement, where, as aforementioned in the prior art, these adjacent marks were covered. 
     FIG. 2 illustrates an instrument  200  of similar embodiment to instrument  100  from a top plan view, with cover  170  removed therefrom. In the instrument  200 , an additional arm structure  180  is provided at one end of guide rule  160 . Arm structure  180  may be permanently affixed, or may be removable therefrom. In the most preferred construction of instrument  200 , arm structure  180  is one-inch wide adjacent to rule  160 . Furthermore, arms  181 ,  182  and  127 ,  128  are each exactly one-half inch wide. By so dimensioning the arms, an inside diameter measurement may be taken and read directly from rule side  162 , using point  150  as the zero marker point. In other words, as shown by the position of body  110  in FIG. 2, an inside diameter measurement of this position would equal exactly three inches. An outside diameter measurement or thickness would equal one inch less, or exactly two inches. Those skilled in the art will readily recognize that other dimensions may be used. Nevertheless, these particular dimensions have been found to be most preferred. 
     FIG. 3 illustrates a third embodiment of the invention which has special vernier inserts  352  and  356  which may be formed separately from body  310  and then attached thereto by, for illustration purposes, screws  357 ,  358 . These separate vemiers  352 ,  356  may be made very precisely, and separately from body  310 , thereby saving the special treatments for only those components that truly require them. In the event of any distortions during heat treatment, the verniers  352 ,  356  may be adjusted by loosening screws  357  and  358  to ensure proper alignment with body  310 . In practice, these verniers  352 ,  356  are most preferably exactly one-half inch offset from leading edge  126 . This placement does not alter the operation of the vernier in any way. 
     Instruments  100 ,  200  and  300  each have a fractional vernier adjacent edge  164  of rule  160 . This vernier is most preferred, but not essential. Adding this fractional vernier allows the single instrument to be used for more diverse measurements. Each instrument  100 ,  200 ,  300  also has a decimal vernier  152 ,  352  adjacent edge  162  of rule  160 . This decimal vernier is formed by dividing three inches into twenty-five equal spaces. These spaces, center-to-center, are then equal to 0.120 inches. On the standard rule, the eighth-inch spacings are equal to 0.125 inches, which means that each vernier increment represents exactly 0.005 inches. This allows the fractional rule to be used to take measurements in thousandths of an inch. Furthermore, the eighth-inch graduations are readily converted by a table, which might, for example be printed directly on the back side of body  110 , into the decimal equivalents of 0.125, 0.250, 0.375, 0.500, 0.626, 0.750, and 0.825 inches. By adding the correct numbers of 0.005 inches, based upon the vernier reading, to the decimal equivalent of the eighth-inch scale, an operator can readily determine measurements in thousandths units. 
     FIGS. 4 a  and  4   b  illustrate another feature of the preferred embodiment, wherein rule graduation marks  410 ,  420  and  420  are adjacent decimal vernier graduation marks  440 ,  450 ,  460 . As shown in FIG. 4 a,  vernier mark  450  is aligned exactly with rule graduation  420 . If each of the graduations on the rule and vernier are exactly 0.005 inches in width, the  0 . 120  inch center to center spacing between marks  440  and  450 , when added to the 0.005 inches width of mark  440 , will bring mark  440  just to the edge of mark  410 , which is 0.125 inches on center from mark  420 . As a result, the edges of marks  440  and  460  will align with the edges of marks  410 ,  430 , as shown therein. 
     As can be seen in FIG. 4 b,  an interpolation feature is also possible when each of the graduation marks  410 - 460  are equal to the difference in center to center spacings between the rule and vernier. As seen therein, when none of the marks exactly align, but two adjacent marks are equidistant between vernier and rule, such as adjacent marks  410 ,  420  which are, in FIG. 4b equidistant to marks  440 ,  450  of the vernier scale, the actual vernier calculation is the average of the two adjacent marks. In other words, the actual vernier distance will be the sum of vernier amounts calculated for mark  440  and  450 , the sum then divided by two. In effect, this allows relatively precise interpolation to 0.0025 inches with consistency. 
     Important is the process for determining the actual graduation mark width. The graduation marks are most preferably exactly equal to the difference in spacing between the vernier and the rule. As long as this is true, this phenomenon of FIG. 4 will then apply to other dimensions besides the eighth-inch rule and five-thousandths vernier of the preferred embodiment. Nevertheless, the eighth-inch unit is the only unit which converts to the desired thousandths precision, so this combination is the most preferred of the present invention. 
     FIG. 5 illustrates by flow chart the process  500  of calculating the decimal vernier in more detail. Therein, the first step  510  is to position the rule relative to one extreme of the distance being measured. This is typically accomplished by placing either an end of the rule or arms such as arms  181 ,  182  against the first extreme edge to be measured. Next, in step  520 , block  110  or  310  will be moved relative to rule  160  until the appropriate feature of the block is adjacent the other extreme edge to be measured. In step  530  the fractional rule is read, making sure that if a measurement is between two fractions, the smaller amount is used as the fractional amount. In other words, if the value is between one-eighth and one quarter of and inch, the one-eight inch value is the one that should be used. That fractional measurement, which will also include whole numbers for the total number of full inches, will be converted to a decimal value in step  540 . This will most preferably be accomplished using a look-up table or chart for each of the seven discrete fractions, though other techniques may be used. 
     The next steps  550  and  560  are listed in sequential order following steps  530  and  540 , but it is important to note that the actual order of these steps is not critical and that steps  550  and  560  could, in fact, come before steps  530  and  540 . In steps  550  and  560 , the vernier marks are compared to the rule fractional graduation marks to find the closest ones. Once that is done, an operator will count from the zero mark vernier graduation the number of vernier graduation marks to the closest mark. This number is multiplied in step  560  by 0.005 to calculate a second decimal value which represents the vernier offset from the fractional distance of step  530 . Once that is done, the first decimal value of step  540  is added to the second decimal value of step  560 , to obtain the full measured distance in decimal format. In the event two marks are equidistant at step  550 , then the average of the two marks must be used to get an accurate measure, as was previously discussed in reference to FIG. 4 b.    
     By placing the graduation marks upon the top surface of the rule and vernier, and keeping these marks closely adjacent, optical alignment and visual determination of precision approaching one-thousandth of an inch are viable. However, the inventors recognize that the principles of this feature of the invention, dividing a fractional rule with a decimal vernier, may be implemented by other methods besides optical and visual discrimination. Other methods may be considered by those skilled in the art, such as electrical or electromagnetic interpolations and digital displays, the use of microprocessors to perform the basic computations illustrated herein for the calculation of the actual distances, and so on. Nevertheless, the preferred embodiment offers the advantages of durability and simplicity, making this construction optimal for a harsh production environment. 
     FIG. 6 illustrates a fourth embodiment instrument  600  which is capable of accurate resolution to one thousandth of an inch. Instrument  600  includes a base  110  into or onto which is attached a special hardened or heat-treated vernier  652 . Rivets, screws or any other suitable fastening means may be employed to retain vernier  652  to base  110 . Most preferably the attachment method allows precise placement or adjustment at the time of manufacture to ensure that vernier  652  is properly aligned with arm  110 . 
     Vernier  652  is similar in arrangement and function to verniers  152 ,  352 . However, vernier  652  illustrates an alternative construction which in this embodiment extends substantially from the measuring surface or zero-point  626  closest to arm structure  180  towards the opposite end of base  110 . This allows vernier  652  to be manufactured separately from base  110 , and enables base  110  to be manufactured at a somewhat lower cost. Further, vernier  652  then takes on a more regular geometry, further simplifying the process of marking or scribing the particular graduations, and thereby typically improving precision and lowering manufacturing costs. Additionally, and as will be described hereinbelow, the verniers are preferably interchangeable with differently marked verniers, allowing diverse applications for the same basic instrument. 
     Preferably, verniers  652  and  656  will be slightly offset from edge  626 , for exemplary purposes by a small amount such as a few thousandths of an inch. This offset helps to prevent the vernier from being accidentally bumped out of proper alignment with base  110  during use. Also, the first mark is fairly difficult in production to position relative to the edge of the vernier, but all other marks are precise relative to the first mark. Consequently, removal of a small amount of material ensures that any imperfection in the distance between edge and first mark is eliminated from interfering with accurate measurement. 
     In instrument  600 , several additional alternatives which differ from earlier described instruments are illustrated, including the use of specially treated measuring surfaces  625  and  683  extending from arms  627 ,  628 ,  681 , and  682 . These may preferably be slightly rounded or domed pins that are also specially hardened or heat treated to reduce any likelihood of deformation during use, though the geometry or material of these pins is not critical to the present invention. These pins may be cast, molded, pressed, threaded or otherwise affixed into arms  627 ,  628 ,  681 , and  682 . Most preferably, and similar to arms  181 ,  182 ,  127 ,  128 , the spacing between these pins is predetermined and accurate, and also most preferably established at a simple fraction or decimal distance. 
     A second vernier  656  is provided parallel to vernier  652  but on a longitudinally extending edge of rule  160  opposite vernier  652 . Vernier  656  is also affixed to base  110 , typically using a similar method of attachment as with vernier  652  to help simplify the number of unique manufacturing processes. Onto vernier  656  are special graduation marks extending from mark  640  to mark  650 , and including mark  630  therebetween. These graduation marks are designed to align with a predetermined fractional unit of measure on rule  160  at only one position within the range of graduations from mark  640  at a first end to mark  650  at a second end. In FIG. 6, which is only exemplary, graduation mark  630  aligns with the eighteen-inch graduation mark on rule  160 . Preferably at consistent intervals, the additional marks from mark  640  to mark  650  are spaced to not quite align with a fractional unit present on rule  160 . More specifically, and using the one-eighth inch markings of rule  160 , the graduation marks from mark  640  to mark  650  will be spaced not the 0.125 inches of one-eighth of an inch, but instead only 0.124 inches. This way, any offset of from +0.005 to −0.005 inch, with resolution to one-thousandth of an inch, can be measured and observed. This can be added to or subtracted from the five-thousandths of an inch resolution measured using vernier  652 . 
     It is noted that the selection of correspondence between the marks from mark  640  to mark  650  to the one-eighth inch graduation marks is not critical to the invention, and that there may instead be correspondence between any other fractions, or even decimals, on rule  160  and graduation marks on vernier  656 . So, for exemplary purposes only, the marks from mark  640  to mark  650  may be spaced using quarter-inch correspondence, in which case the spacing between each adjacent mark from mark  640  to mark  650  would be 0.250 inches less one thousandth, or 0.249 inches. Similar calculations may be made for any other spacing or arrangement of markings that may be selected for rule  160 . In addition, there is no limitation intended or implied on exactly how many marks will exist between marks  640  and  650 , nor, therefore, on whether only one mark will align with a corresponding rule graduation. Furthermore, there are situations where the graduations will not all be equidistantly spaced. For example, and as will be better understood with relation to the description of FIG. 8, it is possible to provide a set of graduations spaced at the “increment less one thousandth” as above, and also provide several spaced at the increment less a different amount, such as five or ten thousandths, or even fractional increments. These additional graduations can then be used to expand the application of a single instrument to serve several diverse purposes, such as measurement and tolerance checks. The use of a total of eleven marks is one of convenience, since vernier  110  has resolution to five-thousandths of an inch. However, as few as five graduation marks will adequately resolve to one-thousandths of an inch. In the simplest use of this combination of five-thousandths vernier  652  and thousandths vernier  656 , the measurement is calculated as described with reference to instruments  100   200 ,  300  to five thousandths. Then the vernier  656  is used to reach final resolution to thousandths simply by adding or subtracting thousandths from the five thousandths total, based upon where vernier  656  graduation marks from  640  to  650  align with rule  160  graduation marks. 
     An alternative application of instrument  600  is illustrated in FIG. 8, which describes a method  800  for determining whether production tolerances have been met. Using method  800 , both base  110  and arm structure  180  are preferably movable relative to rule  160 . Step  810  involves determining an approximation for the measure to be taken or compared against. If there is a blueprint dimension or similar written dimensions to work from, these can be used directly from the print. Otherwise, the approximate measure can be taken with a rule such as rule  160  or with instrument  600 , as desired. This approximate measure may, for example, be the intended dimension of a part to thousandths of an inch, or may instead be the actual measure, estimated to thousandths. 
     Using the approximate measure calculated in step  810 , a truncated inch spacing and decimal remainder will be calculated in step  820 . The truncated inch spacing is obtained by truncating the approximate measure to inches, by dropping off the tenths, hundredths and thousandths. The discarded tenths, hundredths and thousandths become the decimal remainder. 
     In step  830 , edge  626  will be set to an inch spacing from the end of rule  160  which is preferably equal to or greater than the total displacement of arm structure  180 . In the preferred embodiment, this is done by first aligning edge  626  to an inch graduation, and then verifying that the five thousandths vernier  652  and thousandths vernier  656  also confirm exact alignment. In an alternative embodiment, this may be done by releasing arm structure  180  and base  110  sufficiently from rule  160  that they each may slide longitudinally along rule  160 . Rule  160  is then placed normal to a planar surface, and arm structure  180  and base  110  are slid towards the planar surface as far as possible. Next, base  110  may be locked against relative movement with rule  160 . Preferably then,for this alternative embodiment step  830  to work as intended, arm structure  180  will occupy an even number of inches along the longitudinal length of rule  160 , or, in the case of FIG. 6 exactly two inches. Base  110 , after locking, will most preferably exactly align so that the edge  626  aligns with the inch graduation marking on rule  160 , such as the two-inch graduation in FIG. 6, and the 0.125 marking on vernier  652  aligns exactly with the five-inch graduation, and graduation  630  aligns with the nineteen-inch marking. It is very important at this step  830  that the user accurately set base  110  relative to rule  160  at this time. As noted however, in one embodiment this accurate setting of base  110  will simply entail releasing both base  110  and arm structure  180  to slide against a planar surface from which rule  160  extends in a normal (perpendicular) direction, and then locking base  110  against further movement. However, this alternative approach may be less desirable in some instances, since the precision of the instrument is subject to the possibility o grit on the planar surface, and production tolerances on arm structure  180  that may make precise dimensions much more difficult or expensive. 
     In step  840 , a gauge block thickness standard closest to the decimal remainder is selected, and placed between edge  626  and arm structure  180 , and then arm structure  180  is locked into place relative to rule  160 . The selection of a dimension for the gauge block is done based upon the availability of thickness standards to the desired decimal. In other words, if the approximate measure of step  810  is 1.750 inches, then the decimal remainder would be 0.750 inches. If the user possessed a gauge block that was exactly 0.750 inches, which is most preferred, then arm structure  180  will be separated from edge  626  by the 0.750 inch standard and then locked into place. Standard sizes that differ from the decimal remainder may be used as well, but less preferably as will become apparent herein below. 
     In step  850 , base  110  is released to move relative to rule  160 , and is spaced from arm structure  180  by the amount of the distance to be measured. This will typically be done by releasing base  110 , and then using instrument  600  to measure a part in the typical way, such as by inserting the part between edge  626  and the closest surface of arm structure  180 . In step  860 , the five-thousandths vernier  652  will be read, and in step  870  the thousandths vernier  656  will be read. In step  880 , the integer inch offset from edge  626  in step  830  to the position of edge  626  in step  860  is determined. 
     If arm structure  180  was set using a gauge block thickness standard that was exactly equal to the decimal remainder, the integer inch offset determined in step  880  should equal the truncated inch spacing calculated in step  820 . If not, the final part is off by more than one inch from the approximate measure. Typically, in a production environment, determining whether this number matches will not be done since a visual inspection will normally identify a full inch defect. If the standard is exactly equal to the decimal remainder, then the edge  626  will align directly with an inch graduation on rule  160 , and graduation  630  will be very close to or aligned with an inch graduation also. If the part is within five thousandths of an inch, one of the graduation markings between mark  640  and mark  650  will align, and edge  626  or either the next graduation mark (the 0.005 graduation mark) or the 0.120 graduation mark on vernier  652  will align best with the one-eighth inch graduations on rule  160 . 
     If the standard does not exactly equal the decimal remainder, then the user will have to calculate the anticipated additional offset, and read the verniers  652 ,  656  and rule  160  accordingly, to confirm the anticipated placement of each vernier  652 ,  656  with respect to rule  160 . While this approach still works, the review of the offset is slightly more complex and also thereby slightly more prone to being misread. 
     When used to repeatedly determine tolerances of a single production part, instrument  600  may be “preset” by steps  810 - 840 . Then, for each part to be tested, steps  850 - 890  will be conducted. Each time a subsequent part is to be tested, steps  850 - 890  may again be repeated without having to reset or recalibrate in steps  810 - 840 . This simplified testing of multiple parts having the same intended dimensions is shown by answering yes to question  895  in FIG. 8, which returns the user to step  850  for each additional part to be tested. 
     It should now be apparent that by using this method  800 , and once steps  810 - 840  have been completed to preset instrument  600 , a user can quickly determine whether each part is within 0.005 inches of tolerance by simply looking at edge  626  to confirm that the closest mark to edge  626  is the correct inch graduation mark, next confirming that either edge  626  or the 0.005 or 0.120 graduations are closest, and then confirming that one of graduation marks  640  to  650  align with the corresponding marks on rule  160 . If the tolerance window is desired to be greater than the ten thousandths illustrated for instrument  600 , the numbers of marks between  640  and  650 , with each offset from the associated graduation mark of rule  160  equaling an additional one-thousandth of an inch, can be increased, thereby also increasing the total distance between mark  640  and mark  650 . For example, while the illustration of FIG. 6 shows there to be eleven total marks spanning 1.24 inches from mark  640  to mark  650 , thereby permitting a window of plus or minus five thousandths, it would be possible to extend the scale to include twenty-one marks spanning 2.28 inches permitting a window of plus or minus ten thousandths. Furthermore, the distance spanned between marks  640  and  650  is only determined by what fraction or decimal of an inch the marks are selected to correspond to on rule  160 , so the same twenty-one marks would, for example, span only 1.23 inches if the marks were created to correspond to the one-sixteenth inch graduations on rule  160 , instead of the one-eighth inch graduations shown in FIG.  6 . 
     While instrument  600  offers a great deal of versatility in taking accurate measures to thousandths of an inch and also in performing quality control or tolerance checks as illustrated in method  800 , there are times where all of the graduation marks are unnecessary, and a single instrument will be dedicated solely to tolerance testing of a single part. In those instances, an instrument such as instrument  700  shown in FIG. 7 may be preferred, owing to reduced cost and greater ease of use. In such a case, steps  810 - 840  are performed prior to instrument  700  being provided to the user, and the only markings on rule  160  that are necessary will be marks  710  and  720 , which correspond to marks  640 ,  650  of vernier  756 . While not essential to the performance of the invention, it is conceivable that arm structure  180  could be permanently fixed in position relative to rule  760  after initial preset or calibration, or not be adjustable at all. 
     When a part is checked for tolerance using instrument  700 , and also following the examples of FIG. 6 as shown therein and described herein above, if the part has a plus or minus five thousandths of an inch tolerance, then lines  640  and  650  must both stay within the limits which are set by lines  710 ,  720 , just as would have been the case with relation to instrument  600 . Anything else would constitute a part out of tolerance. Other verniers  657 ,  658 ,  752  may be optionally provided, and other graduation markings similar to marks  710 ,  720  may be provided on rule  760  as desired. For example, marks  710 ,  720  may be used to determine the tolerance of one particular dimension in association with marks  640 ,  650 , but a part may have several critical dimensions or several different parts may desirably be checked using instrument  700 . In these instances, additional markings similar to marks  640 ,  650 ,  710 ,  720  may be provided. This allows for some compromise between the simplicity of instrument  700  and the flexibility of instrument  600 . 
     In addition, while dual marks  640 ,  650  on vernier  756  are illustrated, the use of a single mark is contemplated as well, using the single mark to represent the desired distance of measurement, and marks  710 ,  720  then establishing limits of travel from the single mark to remain within tolerance or specification. 
     In yet another alternative embodiment, the uses for standard base  110  and arm structure  180  may be expanded without having to replace base  110  and arm structure  180 . In this manifestation, different verniers may be added to or removed from base  110  and arm structure  180 , similar to the replacement of verniers  652 ,  656  with verniers  752 ,  756  of FIG.  7 . The changing of verniers allows a single base structure to be used in the taking measurements or alternative testing for tolerance in a “go-no go” manner, simply by changing out the verniers or the verniers and rule. 
     While the foregoing details what is felt to be the preferred embodiment of the invention, no material limitations to the scope of the claimed invention are intended. Further, features and design alternatives that would be obvious to one of ordinary skill in the art are considered to be incorporated herein. The scope of the invention is set forth and particularly described in the claims hereinbelow.