Abstract: A pocket tide calculator is described which predicts tide times and moon phases in a visual display which gives the semi-diurnal tide times in any given day of the month and can be readily set for the following month. This device automatically leaves out the high or low tide which is alternately missing every 7.5 days. This invention incorporates a compressed time scale when compared with a normal 24-hour clock face which enables a concise display of the semi-diurnal tide cycle.

Abstract: An indicating device (2) for indicating dates upon which events such as procedural steps should take place, said device (2) comprising a first disc (4) having a first field )24) which includes a plurality of first dates and at least one second field (26) which includes a plurality of second dates, the positions of said fields (24, 26) having a predetermined relationship to one another on the first disc, a second disc (6) pivotally connected for relative rotary movement to the first disc (4), the second disc having a first window (12) which can be aligned with a selected one of the first dates and a second window (14, 16, 18, 20) having a predetermined position relative to the first window, the arrangement being such that when the first window is aligned with one of the first dates, the second window is aligned with a second date in the second field thereby indicating the date upon which an event should take place consequent upon selection of one of the first dates.

Abstract: An improved IC card construction eliminates the need for a frame thereby increasing the space available within the IC card and the available substrate or PCB surface area making possible the use of additional integrated circuits or other electronic components. The frameless IC card of the invention includes a housing comprising top and bottom covers having interconnected longitudinal side margins providing a rigid IC card housing structure.

Abstract: A golf round timing device is provided for determining the time at which a golfer is to start a golf hole. The golf round timing device comprises a base and a circular disk member. The base has an outer arcuate row of indicia, indicative of time intervals, disposed thereon. The circular disk member has a smaller radius than the outer arcuate row and is rotatably mounted at a mounting point on the base in such a fashion as to be concentric with the outer arcuate row of indicia. The circular disk member has at least one inner arcuate row of indicia indicative of holes on a golf course so that when the inner arcuate row of indicia is aligned with the outer arcuate row of indicia, the time at which the golfer is to start a golf hole may be determined.

Abstract: The amount of recording time remaining on a partially recorded videotape cassette (11) is measured by fixing the position of a body member (17, 117) relative to the hub (14) of a cassette reel, and moving a pointer (24, 120) to point to the outermost layer (33) of tape (12) wrapped around the hub (14). Movement of the pointer relative to the body member causes corresponding movement of an index (38, 145) relative to a time scale (39, 125), so that the remaining time can be read off the scale. The pointer is coupled so that small movement of the pointer relative to the body member, causes large movement of the index relative to the scale. In one embodiment, a transparent disc pointer (17) is coaxially attached to a transparent disc body member (24).

Abstract: An apparatus for identifying the optimum jet for a carburetor which includes a general annular first member having a plurality of first graduations disposed about a peripheral portion thereof, a general arcuate second member having a plurality of second graduations disposed for cooperation with the first graduations, and members coupling the first and second member permitting relative rotation and selective alignment of the first and second graduations. One of the plurality of graduations are arrayed on a linear scale corresponding to relative air density and the other of the plurality of graduations being arrayed on a scale corresponding to respective jet flow and or identifying numbers. The members coupling the first and second members may include a plurality of arms disposed at angularly space intervals. There may be three such arms and they may be fixed to the arcuate member. The annular member may include an offset peripheral portion that is nested between with the three arms.

Abstract: A calendar date finder in the form of a circular slide rule composed of two interacting disks, rotation of one disk relative to the other selectively providing calendar date information from a first preselected year through a second preselected year, inclusive. An upper disk has a circular periphery with a notch along a portion thereof, and further has a cut-out spaced uniformly from the periphery and extending along a portion of the periphery. Numeric indicia are printed on the upper disk adjacent the notch. The numeric indicia are sequential numbers from 1 to 31 representing the thirty-one days of a calendar month. Month indicia are printed on the upper disk in a predetermined pattern adjacent the cut-out. A lower disk has week day indicia printed thereon uniformly spaced along the periphery thereof, in a sequential pattern. Spaced inwardly from the week day indicia is a predetermined pattern of year indicia indicating each year from the first through the second preselected years, inclusive.

Abstract: A method for determining the spacing between adjacent vantage points for taking a 3-D photograph which involves computing the desired spatial parallax in accordance with the following formula: ##EQU1## where P is the desired spatial parallax, V is the viewing distance and E is the capability of the eyes to fuse the two images together expressed in terms of arc minutes of the scanning angle and utilizing results of this computation to compute the distance T between adjacent vantage points in accordance with the following formula: ##EQU2## where B is the distance between the camera and the background object and K is the distance between the camera and the key subject and u is the back focal length of the camera lens. A calculator has been provided for making the necessary calculations.

Abstract: A device for assisting a computer operator in the use of computer programs includes relatively movable cards bearing data areas thereon arranged in such a way that the operator can, firstly, by visual inspection, readily locate the desired operation to be performed by the program and, secondly, by moving the cards relative to one another, obtain, for that desired operation, information regarding the command to be entered into the computer.

Abstract: A fluoride supplement calculator utilizes two concentrically positioned relatively rotatable disks. A front disk has a plurality of fluoride level apertures which overlie groups of fluoride dosage amounts carried on the second disk. An age scale is also placed on the obverse surface of the second disk. The second disk has a single aperture which is used in conjunction with the reverse surface of the first disk to depict fluoride uptake and enamel formation in teeth of patients of various ages.

Abstract: Disclosed is a diving computer in the form of a circular slide rule for aiding a SCUBA diver in planning one or more dives within a short amount of time, including more than one depth per dive, so that the diver may avoid risking decompression sickness. The computer has two faces, one of which calculates the increase of pressure within body tissues during a dive and the other of which calculates the decrease of this pressure after surfacing. The result of one side's calculation is used as the initial value for the other side's calculation, permitting the diver to track net residual pressure over a series of rapid repeated and/or multiple-level dives, and by so doing, avoid excessive tissue pressures that might cause decompression sickness.

Abstract: An alcoholic concentration indicator comprising three superposed circular discs adapted to rotate about a common axis. The lower disc displays on its margin a scale of alcohol concentration indicia and over its central surface a multiplicity of numbers representing the number of drinks consumed. The middle disc has a series of aperture across a diameter to provide usual access to the numbers appearing on the central portion of the first disc. Each aperture is identified by a weight of a human body. A scale of consecutive numbers also appears to represent the number of hours elapsed since the first drink. The top disc is transparent and displays two pointers: one pointer for the alcoholic indicia and the other pointer for the time elapsed since the first drink. The desired results are obtained by visualizing the number corresponding to the number of drinks through the aperture corresponding to the weight of the user.

Abstract: Apparatus for use in correlating actual tape play times, tape length, or predetermined tape program locations with tape-spool revolution values provided by a tape-revolution index counter in a tape machine. The calculator has a lower circular base plate and a smaller, upper circular plate which rotates concentrically with respect to the lower plate. The base plate carries a scale corresponding to tape-spool revolution values indicated by the machine, and one or more time scales relating tape spool revolution values to actual tape-play times, and/or to remaining play times or program locations. A ratio marker and time scale indicator are positioned on the upper member such that alignment of the ratio marker with a selected tape-revolution value on the base plate brings the time scale indicator into alignment with the corresponding playing-time value on the base plate.

Abstract: A time period calculator employing a base, a calendar disc, a calculation disc and a cursor. The calendar disc includes divisions identified by months and days of the year about a common axis. The calculation disc is divided into increments of time in days, weeks and months from zero consecutively in both clockwise and counterclockwise directions for measuring time periods prospectively and retrospectively, respectively. The base may include divisions divided into 1/365th segments with day of the week indications thereon. The cursor includes line segments offset over the calendar disc divisions by one day so as to accommodate leap year calculations.

Abstract: A vehicle performance computer for determining the performance parameters of a vehicle including: a substantially planer base having logarithmic scales representing speed, weight-to-horsepower, distance, and time arcuately disposed about a center; a substantially planar intermediate slide having logarithmic scales representing percent grade, speed factor, and top time and distance percent grades in proporation to the percent grade scale and arcuately disposed about a center; and a substantially planer top slide having logarithmic scales representing speed factors in relation to time and distance scales and arcuately disposed about a center. All three planer members are rotatably connected one to another coaxially about the three centers with the intermediate slide lying between the base and top slide. The intermediate scale also includes a window arcuately disposed about the center for viewing the weight-to-horsepower scale in relation to the percent grade scale.

Abstract: The Heat Stress Calculator is a manually operated, mechanical computer and program for determining human thermal discomfort or heat stress, reported as an equivalent heat stress temperature (HST), for any given summer air temperature, relative humidity, wind velocity, sky condition, time-of-day, terrain, and individual physical activity level. The calculator consists of six circular and partial discs concentrically mounted for adjustment of their scales by rotation to various positions relative to each other and to stationary front and back windowed panels. The Heat Stress Temperature is the equivalent air temperature under standard moderate thermal and activity conditions that would result in the same heat stress produced by the actual conditions experienced.

Abstract: An aliquot part subdivision locator assigns reference numerals to each of 64, (or other power of 4) subdivisions of a square representing an aliquot part or an aliquot part subdivision. A chart matches each subdivision's label with a reference numeral, and two labelled discs having holes therein are set with a reference numeral aligned. When a reference numeral of the lower disc is aligned with the same reference numeral on the upper disc, and when both discs are at a predetermined angle relative to a randomly chosen radius, the aligned reference numeral appear through the holes at the appropriate position of a map in front of both discs.

Abstract: A slide-rule is obtained by superpositioning and connecting three plates (1, 2, 3) into the middle one of which slots (20, 21) are milled, and thereafter cutting off the boundary areas (5, 6, 7, 8), including the boundary areas (5, 6) of the middle plate (2), into which the slots (20, 21) do not extend.

Abstract: This invention is a calculator that is particularly adapted to assist the user thereof in determining the location of waterfowl decoys relative to a duck blind. The calculator can be adjusted as wind direction dictates to give varying patterns under varying wind speeds and directions.

Abstract: A device to display musical chords and notes for fretted string instruments comprising (a) top sheet having a plurality of transparent patterns representing the strings and frets on the fingerboard of the instrument, (b) pivot located at a central point on the sheet, and (c) underlying rotatable disk having a plurality of patterns of spots representing different types of chords. All the fingerboard patterns on the top sheet are identical but each is disposed to display chords in a different musical key. When the rotatable disk is angularly indexed relative to the top sheet, the device displays a plurality of musical chords, differing in position on the fingerboard, in musical key and in chord type. The spots displayed through the transparent fingerboard patterns indicate where the fingers may be placed on the strings and which strings may be left unstopped when a chord is sounded.

Abstract: A convenient, easy-to-use calculator computes a person's proper bra and cup size given a knowledge of that person's chest, overbust, and band measurements. The calculator comprises a circular slide rule of three superimposed disks, the intermediate disk being of larger diameter than the upper disk and the lower disk being of larger diameter than the intermediate disk. The three disks are mounted for relative rotation by means of an axially disposed pivot, pin, rivet, or other means transfixing the disks for ease of rotation about their centers. Scalar indicia at the periphery of the disks represent body measurements required for the determination of proper bra size. Proper bra and cup size are viewable through circular indexes when a person's chest and overbust measurements are aligned on the two outermost peripheral scales and the person's underbust or band measurement is aligned with a fixed index on the intermediate disk.

Abstract: A method of fabricating a hand calculator utilizing die press punching to form its three parts. A circular stationary base plate is punched with a central, circular, raised, beveled portion which is then rigidly fixed to a circular stationary top plate by means of flared eyelets. Between these two parts a circular movable scale plate is movably inserted. The scale is etched with scales, and punched with a plurality of holes about its periphery to allow for pencil point movement.

Abstract: A color computer wheel includes a white base member upon which four concentrically arranged discs are rotatably mounted by a central fastener, the discs decreasing in diameter from bottom to top and being made of a transparent sheet material. The top disc carries four concentric annular bands, each evenly divided into radial spaces. The three lower discs are each dedicated to a single primary color, and carry color bands arranged to register with the bands of the topmost disc, the color bands being divided evenly into radial spaces with progressive color shades thereon. The peripheries of the four discs carry legend strips, which identify the percentage of color in the radial spaces in alignment therewith.

Abstract: A storeroom bin marker which includes a base member having indicia thereon, and a rotatable view blocking member which can be selectively rotated to cover some, all, or none of the indicia, to thereby indicate the supply or reorder status of a stocked item. The base member has front and top panels at right angles with respect to each other, and is designed to fit over the front and top edges of a storage shelf. The bin marker has mounting holes in its front and top panels which can be used, with an elastic cord member, to secure the bin marker to wire shelves; or which can be used with screws to secure the bin marker to a solid shelf. Alternatively, the bin marker can be adhesively mounted to solid shelves. The front panel of the bin marker is provided with a pair of parallel, spaced apart bin label retainers for releasably holding a replaceable bin label.

Abstract: A calculating device and a method of use thereof for determining the lead required to shoot a projectile at a moving target including cooperating logarithmic scales with indicia corresponding to the parameters target speed, range, projectile speed and lead displayed on a fixed and a slide member. Pictorial markers representative of various projectiles are disposed along the projectile velocity scale at locations corresponding to their normal speed and words descriptive of target speed are disposed at appropriate locations along the target speed scale so that calculations may be made by persons not having knowledge of game and projectile speeds in numerical terms. In accordance with one embodiment of the invention, the logarithmic scales are longitudinally disposed and the slide member may move relative to the fixed member in a horizontal direction. In accordance with other embodiments of the invention, the scales are disposed in a circular arc on members which may be rotated about a common axis.

Abstract: The Camera Setting Calculator for Underwater Color Photography is a manual, mechanical calculator to be used in determining the aperture setting (f-number) of a camera and consisting of two circular sheets of data pivoted to rotate over each other. Rotation of the top piece inputs the given data and displays the appropriate f-number.

Abstract: A device for converting between the metric and English systems of measurement including a circular scale disc having concentric scales on one side graduated according to the English system and correlated concentric scales on the opposite sides graduated according to the metric system. A pivoted cursor straddles both sides of the device and has index windows through which related English system and metric system measurements may be read, the scales being correlated so that one index window exhibits an amount according to the English system and the other exhibits a corresponding amount according to the metric system. Certain scales in the metric system have dual functions. A measuring tape is received in a cavity formed in two facing side discs and is moveable endwise in slots formed in the side discs, the tape being marked off according to both the English and the metric system.

Abstract: A hand-operated musical rhythm pattern generator includes two independently rotatable discs mounted in a holder. The discs have complementary rhythm patterns printed on the peripheries thereof, a portion of which is visible through a window in the holder. The rhythm patterns displayed may be randomly changed by rotating one or both discs any desired angular amount.

Abstract: A calculating device and a method of use thereof for determining the lead required to shoot a projectile at a moving target such as game including cooperating logarithmic scales with parameter indicia corresponding to the range of the target, the speed and direction of movement of the target, the speed of the projectile and the required lead displayed on a fixed and a slide member. Markers representative of various projectiles are disposed on the projectile velocity scale at locations corresponding to their normal speed and words descriptive of game speed are disposed at appropriate locations along the target speed scale so that calculations may be made by persons not having knowledge of game and projectile speeds in numerical terms. The lead is calculated from a knowledge of the parameters in a two step process of moving one member relative to the other. In accordance with one embodiment of the invention, the scales are arcuately disposed on members which may be rotated about a common axis.

Abstract: Method and apparatus for copy-fitting, using a new parameter called Font ID in a circular calculator having a plurality of relatively rotatable disks, some of which have cursors affixed thereto, and one or more freely rotatable cursors. Scales on the several disks include Font ID numbers, type size, in points; line length, in picas; number of characters per line; number of characters per page; page depth in picas and number of lines; and line spacing in points.

Abstract: A tidal time indicator for determining tide times at various locations on a specific stretch of coastline comprises a pair of complementary charts. One of the charts is in the form of a map having index marks representing the various locations and which marks are spaced apart at distances corresponding to the known tidal time differences between the particular locations. The other chart is in the form of a rule having a time scale and index marks representing different days, each of these index marks being positioned relative to the time scale at the high or low tide time on the particular day for a reference location on the map chart. Thus, by positioning the rule chart relative to the map chart so as to register a date mark with an index mark on the map chart representing the reference location, the tide times at the other map locations can be read directly off the time scale adjacent their respective index marks on the map. To prepare the charts, information is obtained from Tide Tables.

Abstract: A race horse selector includes three discs mounted on a common pivot pin behind a cover disc. Different sized discs are used to expose the outer margins. The margins are divided into equal sectors and numbers 1-12 randomly distributed thereon. The cover member has four spaced openings, one spanning all three discs to identify the win, place and show horses, and/or a Trifector race selection, an opposite one spanning the two outer discs to identify a Quinella or Perfecta race selection and two intermediate openings exposing the smallest and largest discs to identify the second half of a Daily Double and other selections. A locating tab on each disc extends radially outwardly of the cover disc with an outer clamp member extended back over or into the cover disc. Locating indicia on the back permits positioning the tabs such that a number sector is aligned within the openings, without viewing the openings.

Abstract: Method and apparatus for copy-fitting, using a new parameter called Font ID in a circular calculator having a plurality of relatively rotatable disks, some of which have cursors affixed thereto, and one or more freely rotatable cursors. Scales on the several disks include Font ID numbers, type size, in points; line length, in picas; number of characters per line; number of characters per page; page depth in picas and number of lines; and line spacing in points.

Abstract: There is disclosed a marine navigational calculator device of the slide rule type whereby tidal depths over bottom structures may be determined as a function of the time of the tide or time of calendar day and whereby the entire time span available to a mariner to successfully negotiate such charted bottom structures for a given tidal flow is visually presented.

Abstract: "DIAL-A-METRIC" is a measuring device with top and bottom rotating dials and a stationary center dial inscribed with six calibrated scales on two sides. The top and bottom dials have three die cut hairline windows on each side. When the two dials are rotated, the six windows reveal twelve different calibrated scales that converts existing American weights and measures to the International metric system.

Abstract: A portable device to determine highway marker locations including an enlarged disc dial having graduated scale markings on each side thereof and therearound representing increasing and decreasing highway mileage markers, respectively, and smaller disc dials superposed on either side of and centrally rotatably and lockably mounted thereon. The latter are provided with scale markings therearound representing vehicle odometer readings. To keep track of a vehicle's highway location, the user visually notes the last highway marker passed and rotates the small dial until the last two digits of the vehicle odometer reading indicated on the dial scale are aligned with the scale marking on the appropriate large intermediate dial (either increasing or decreasing, depending on direction of travel) corresponding with that mile marker, and the three discs are locked thereat.

Abstract: An improved circular sliderule for use in many applications wherein it is desired to provide a sliderule having superimposed disc elements which may be freely rotated without disturbing the previous setting of the adjacent discs. The novel improved calculator comprises providing a separating spacer element to be positioned between each disc of the calculator and with each spacer element having formed thereon means for retaining the rotation of the spacer element whenever superimposed discs are rotated. The retaining means may comprise a series of protruding arms, one extending outward from each of the separating spacer elements, joined at their outer ends and locked to the base plate of the calculator which is not rotatable. Alternately the retaining means may comprise the spacer element having formed on an internal hole at least one protuberance which is designed for mating engagement with an engaging means in the form of an elongated slot formed in the central hub which is locked to the baseplate.

Abstract: An adjustable display having interworking parts whereby upon manipulation interference frequencies emitted from spurious harmonic and imaged electromagnetic radiators interfering with an intended or expected bracketed received frequency can be isolated and identified for later corrective action, such as elimination of the interference frequencies. A method for establishing emitted frequencies which might interfere with expected or intended targeted received frequencies in a receiver is also described and taught.

Abstract: Calculating device provided with scales for calculating radioactive doses and intensities, in which the scales are arranged for calculating the product of the intensity in a radioactive area at a given instant and a dose factor to be determined by experiment. This dose factor depends on the moment when the contaminated area is entered and on the time spent in the area.

Abstract: An electrochemical grinding process is controlled by the use of a feed-rate indicating device which calculates and displaces the feed-rate (V) of a workpiece and a grinding wheel which are displaced relatively toward one another. The feed rate V is determined by the relationshipV = A p/h + B/.sqroot.hwhere h is the cutting depth, p is the force for driving the wheel electrode in terms of nominal kilowatt power rating P per unit width w of the cutting area, and A and B are constants. These constants are determined between values of A of 150 to 156, exclusive, and values of B from 5.8 to 11.4, exclusive for current densities of 60 to 80 amperes cm.sup.2, respectively, by extrapolation.

Abstract: An X-ray caliper is disclosed having upper, intermediate, and lower discs movable relative to each other, the upper and lower discs have arms extending therefrom between which the part of the anatomy to be x-rayed is positioned, the upper disc has a chart thereon of electrical current versus time and the intermediate disc has on the top surface thereof scales of peak kilovoltages and on the lower surface thereof a listing of various parts of the anatomy. When the part of the anatomy to be x-rayed has been measured and that part listed on the intermediate disc has been positioned relative to the lower disc, the peak kilovoltage range will appear opposite the chart on the upper disc and values of time, electrical current and the product thereof for various kilovoltages can be read therefrom for setting an x-ray machine. The chart can also be moved relative to the upper disc.

Abstract: A hand-held weight control calculator which allows an individual to quickly and accurately determine the daily maximum food calories allowed for either maintaining body weight or for losing a particular number of pounds as a function of individual weight and activity level. The calculator includes a first indicia bearing disc having a plurality of radially arranged columns displaying daily calorie values disposed on its surface, with each column having a peripheral heading designating an individual weight range value and a registration arrow. A second smaller diameter disc is affixed to the center of the larger disc so that they rotate relative to each other, with the smaller disc including an observation window which is selectively registrable with a particular radial column disposed on the larger disc.

Abstract: A global time system having a first disc divided into twenty-four equal sections, each section being formed by lines extending radially from the center of the first disc. Each line forming the sections representing a line of longitude. Circles are concentrically disposed about the center of the disc and extend outward to the edge of the disc. The circles, representing lines of latitude, cross over each of the twenty-four lines of longitude to form geographic spaces between the lines of longitude and latitude. A time disc is rotatably mounted to the center of the first disc and has twenty-four lines equally spaced from each other on the outside edge. Reference symbols are positioned on the first disc and adjacent to the outside edge of the time disc, with the reference symbol in each of the twenty-four sections. Identification symbols representing a specific geographic location are disposed within the respective geographic space having the proper longitude and latitude of the location.

Abstract: A circular slide rule is provided suitable for use in a method determining the electrolyte deficiency in the extra-cellular space from the measured electrolyte deficiency per volume of serum, body weight and body height, and is a method of determining electrolyte deficiency therewith. The circular slide rule comprises a basic disc, a centrally rotatable first rotary disc supported on one side of the basic disc but having a smaller diameter than the basic disc and a centrally rotatable second rotary disc supported on the side of the basic disc opposite to that of the first rotary disc but having a diameter smaller than that of the basic disc. Substantially straight cursors are also provided, each being rotatably supported on one of the rotary discs relative to the appropriate rotary disc and with respect to the basic disc, each said cursor extending at least to the circumference of the basic disc.

Abstract: A chord inversion coordination aid comprises a plurality of dials of increasing diameter and each representing a particular chord type and having a peripheral array of the scale tone names of the chord in its root and inverted positions arranged in sectors, whereby upon aligning various sectors of the discs a given chord progression can be arranged according to the most easily played chord inversions. The dial may be centrally pivoted behind a cover sheet having a window therein to expose the dial sectors, and a pad of staff paper may be mounted on the cover sheet.

Abstract: A laser system computer in the preferred form of a hand-holdable, two-sided circular slide rule, for quickly and accurately solving a wide range of problems which are associated with laser radar, designation, communications and directed energy applications, the solution of which said problems could not be attained with prior art slide rules of any type. Calculations relating to the design, analysis and performance of lasers are performed on one side of the calculator. Atmospheric effects, such as attenuation and turbulence beam spreading, are computed on the other side of the calculator. Both continuous wave and pulsed lasers can be calculated with the use of this unique computer, which also may be used for ground, air and space laser applications. Structurally, the preferred embodiment is in the form of a circular slide rule having: a circular stator (i.e., base) with a front face and a rear face; a plurality of concentric discs (i.e.

Abstract: A musical information display device includes first and second relatively rotatable members, the first member bearing spaced musical indicia and the second member including apertures registrable with the first member indicia on such rotation and aperture-closing elements, each operable independently of the condition of closure of the remainder of such elements. The musical indicia are arranged in such progression as the chromatic scale and numeric identifiers are associated with the aperture-closing elements and are arranged in sequential order to be displayed selectively on operation of the aperture-closing elements.

Abstract: A rotary calculator is disclosed for use in site grading applications and other surveying operations involving the conversion of rod readings to datum or sea level elevations, the determination of depths of cut or fill required for finish grading, and the calculation of material quantities to be moved. The baseplate of the calculator is provided with an annular rod reading scale, and a circular conversion unit is concentrically mounted on the baseplate within the rod reading scale. The unit employs three annular elevation scales covering the units and tens digits, the hundreds digit, and the thousands digit of elevation respectively, and three independently rotatable, coaxial discs align the elevation scales in a manner to convert rod readings radially aligned with the units and tens scale into corresponding elevations relative to a predetermined reference elevation, such as mean sea level.