US 2393922 A Abstract available in Claims available in Description (OCR text may contain errors) Jan. 29, 1946,v H. G, `MDQwl-:LL 2,393,922 CALCULATOR I Filed June 9, 1943 2 Sheets-Sheet 1 Jan. 29, 1946. CALCULATOR Filed June 9, 1943 2 Sheets-Sheet 2 H. G. McDowELL 2,393,922 Patenteci Jan. 29, 1946 UNITED STATES PATENT OFFICE i CALCULATOR Harvey G. McDowell, Wilmington, Del. Application June 9, 1943, Serial No. 490,185 3 Claims. The present invention relates to a calculating device, particularly adapted for use in papermaking plants in connection with the drying end of a paper-making line. In the production of paper, a continuous web is delivered from the wet end of the line, to a plurality of driers, so that the wet web is rapidly dried as it moves continuously through the apparatus. In the drying of the paper, there are a number of variable features which must be taken into account. In the past, it has been the practice to control lthese variables by the skill and experience of the operators or by complicated and involved mathematical calculations, or both. 'Ihe primary object of the present invention is to provide a calculating device which will automatically and expeditiously indicate t the 'operator, the relationship between these variable factors and which will instruct him, substantially instantaneously, exactly how each variable factor under his control should be adjusted for maximum efficiency of the paper-producing apparatus. Operators skilled in the paper-making art appreciate that a predetermined amount of heat must be applied to a predetermined amount of wet paper web, in order effectively to dry the same. The amount of heat applied to a moving web is a function of the number of drying rolls in the drying end of the line, the temperatures of the rolls and the speed of movement of the sheet. As the weight of the sheet increases or decreases, one or more of these factors must be increased or decreased. Similarly, if the weight remains constant and one or another of the variables changes, the others, or at least one of them, must be correspondingly changed. For instance, if the temperature of the rolls is decreased, while' the weight of the web remains confactors can be determined, substantially instantaneously, thereby avoiding reliance upon the stant, the speed of movement of the web must be decreased or the number of rolls employed in the line increased. Similarly, if the number of rolls is decreased, for one reason or another, the temperature of the remaining rolls must be raised or the speed decreased. When the wet end of the machine is changed from one weight of paper to another, corresponding adjustments must be made in the number of drying rolls employed, the temperature to which the rolls are heated, and/or the speed of movement of the web. As stated above, these adjustments have, heretofore, been made as a result of the instinctive skill of the operator and by mathematical calculation, or both. f The present invention provides an apparatus whereby the relationship between these variable skill of the operator and entirely eliminating the necessity for mathematical calculations. The invention also provides means for calculating the production rate of the mill in tons per hour and tons per twenty-four hours, depending upon the weight of the paper, its speed of movement through the driers, and the trim or width of the nished sheet. If the weight of the web and its speed ofmovement are known, the calculator of the present invention vimmediately indicates the production in tons per hour and in tons per twenty-four hours of finished product, for all possible trim widths, thereby eliminating involved, complicated and laborious calculations. Conversely, if a particular production goal is set, for a particular trim and weight of paper, the calculator of the present invention will substantially instantaneously advise the operator as to the speed of movement of the web required to meet this goal. Finally, and without manipulating the calculator, the steam pressure (temperature) and the particular number of rolls needed in operation in the line to maintain this production rate may be immediately determined. Thus, the object of the present invention is to provide a calculator which, by simple adjustment, indicates all possible combinations of adjustments and variations of the several variable factors involved in the operation of drying paper.r Since these variable factors bear a direct ratio or a direct inverse ratio to one another, the calculator of lthe present invention has been bas/ed upon the principle of the slide rule, modified so as to make it correspond to the variables in'- volved, whose ratios have -been determined-by careful observation and calculation.' These variables and their relationship to each other'have been translated into logarithmic scales, yjuxtaposed upon a stationary base or stock and amovable member or slide. For the sake of convenience, and conservation of space, the divisions of the scales have been arranged on radii of a circle, spaced apart in degrees and functions of degrees generally corresponding to logarithmic spacings on a straight slide rule. The movable member has similar scales thereon, and is mounted for rotation relative to the base. A preferred form of the invention is illustrated in the accompanying drawings, Ibut it must be understood that the invention is not limited to the arrangement of parts shown therein and described below, since an almost innite number oi' variations in structure and scales can be sub-l stituted by those skilled in the art, from a consideration of this disclosure. All such variations as come within the scope of the appended claims are intended to be included. In the drawings: Figure 1 is a plan view of the calculator of the present invention. Figure 2 is a section on line 2--2 of Figure 1, and Figure 3 is a plan viewv of the base or stock, with the rotatable slide removed. The calculator comprises a base II! which may be made of any suitable sheet material, such as metal, cardboard, celluloid, synthetic resin or any other plastic. The base carries a stud II, upon which the slide or movable member I2, made of similar sheet material, is mounted for rotation. The -base is provided with a plurality of scales arranged on concentric arcs, all struck about the center of the stud II and each having the individual markings thereof spaced varying distances from one end, in accordance with the principle of the well known logarithmic scales used in slide rules. For purposes of making` the calculations described above, these scales may include a scale I5, having numerals associated with the various markings to indicate the speed of travel of the paper web in units of 100 feet per minute, as indicated by the legend I6 adjacent the scale. A similar logarithmic scale I1, which may be spaced radially outwardly with respect t the scale I6, may have markings to indicate tons of paper produced per hour, and an appropriate legend I8 may be associated therewith. A third scale I9, preferably positioned radially inwardly of the scale I and opposite the scale Il, may be marked to indicate various numbers of hundreds o-f tons of paper produced per twenty-four hours, as indicated by the legend 20. The fourth scale 2I, comprising elongated radial lines 22, spaced apart in a similar manner, according to the logarithmic scale principle, indicates various numbers of drying rolls employed, from fifty to one hundred, the legend 23 for this scale, however, being positioned upon the rotatable slide I2. The radial lines 22 of the scale 2|, for purposes hereinafter described, are intersected Iby a plurality of arcs 2529, both inclusive, adapted to co-nstitute continuations of similarly positioned arcs 25a-29a, both inclusive, on the rotatable slide I2 and each leading to an indicia 30 for a particular steam pressure, as indicated by the legend 3| on the rotatable slide. The rotatable slide l 2 preferably takes the form of a disc made of any suitable sheet material, preferably corresponding to that of the base, and having arcuate peripheral edges 35, 36 struck about the center II, but spaced dierent distances therefrom and connected to each other by angular edges 31, 38. The disc also has two arcuate openings or windows 40, 4I formed therein, in order to expose the scales I9 and 2I, respectively. The opening 40 is in the form of an elongated concentric arcuate slot, while the opening 4I has one end defined by concentric arcs and another, pointed end defined by an angularly disposed and an arcuate margin, for purposes hereinafter explained. The upper portion of the disc, in the space between the cut-outl and the outer margin 36 is provided with a logarithmic scale I5 having numerals 46 corresponding to various widths of trimmed paper in inches, which may beproduced in the mill from one hundred and fifty to two hundred and thirty inches. as indicated by the legend 41. It should be noted that the markings in this scale are the same on both edges and that they are adapted to register with the scales I1 and I9, respectively, indicating the production in tons per hour and in hundreds of tons per twenty-four hours. The arcuate margin Il of the disc I2 is provided with a scale 5l, having numerals II associated therewith, indicating various weights of paper produced in the mill, by the conventional designation of weight per one thousand square feet, as indicated by the legend 5l. The mark ings on the scale 5I are positioned adjacent to and are adapted to register with the markings on the scale I5, indicating the speed of travel of the paper sheet per minute in units of one hundred feet. As stated above, the disc I2 also carries a column of figures 30 for various roll temperatures, translated into the more convenient form of steam pressure in pounds per square inch, and arcuate lines 25a-28a lead from these numbers toward the radial lines 22 associated with the drying roll scale 2I. The expedient shown has been adopted for convenience, in place of having the steam pressure or temperature scale arranged along an arcuate curve, in a manner similar to the other scales, but it will be noted that each line 25a-29a terminates on the straight angular edge 55 of the opening II at a point disposed on a radius spaced circumferentially from the next adjacent radius in accordance with the spacing of a logarithmic scale. Hence, when any particular point of intersection between a line 25a-29a and the margin 55 is brought into registration with a radial line 22, corresponding to a particular number of operative drying rolls, the disc is adjusted with respect to the base in the same manner as if an arcuate scale along an inner or outer margin of the cut-out 4I had been provided. The outer margin of the cut-out 4I is disposed upon concentric inner and outer arcs 56, 51, connected by a straight, angular edge 5B, having indicia 59 disposed therealons, representing various efficiencies, as hereinafter explained and as indicated by the legend 60. It will be noted that the scales for the different variable factors which have a direct relation to each other are disposed in juxtaposition on the base I0 and the rotatable disc I2. The production in tons per hour and in hundreds of tons per twenty-four hours obviously depends upon the width of the paper sheet. Hence, the scale 45, indicating trim in inches, is positioned to register with the production rate in tons and hundreds of tons. As a result, for any particular setting of the rotatable disc, corresponding to a particular combination of speed of travel and paper weight, it is possible to read, adjacent the illure corresponding to the trim being produced, the rate of production in tons per hour and hundreds of tons per twenty-four hours. Similarly, the weight of the paper and the speed of movement of the sheet are in inverse ratio, when the steam pressure and number of rolls are held constant. Therefore, all combinations of weights and speeds may be read at a glance, by comparing the markings on the weight scale 50 with the markings on the speed scale I5. The number of drying rolls and the temperature of the rolls similarly are in inverse ratio, since as the number of rolls is decreased, the temperature must be increased. Hence, the temperaturev scale, lprovided by the vpoints of junction o! the lines 29d-29a with the margin l. of the opening II, is positioned to register withthe scale :I for the number of drying rolls. For any setting of the rotatable slide, it is, thereforefpgssible to read all combinations oi drying. temperatures or steam pressures and numbers oi' drying rolls. The manner in which the various scales were computed and laid out will be briefly described. The divisions oi' the various scales are similar to logarithmic scales on a slide rule, except that they are measured in degrees of a circle instead of in inches. For example, in each oi' the scales I9 and I1, the graduation marked 2 is placed at 30.1, from an imaginary starting point, since the logarithm of 2 is 301. Similarly, the graduation marked 3 is placed at 47.7, corresponding to the logarithmic 477 for the number 3. However, since the spacing of the division and sub-division lines would be quite minute in certain instancesall of the degrees have been multiplied by 3. The markings in the scale 2| for 50 to 100 driers, both inclusive, correspond to the logarithmic values, as indicated by a particular steam pressure. 'This value is directly proportional to the number of driers employed, since 100 driers have twice the drying capacity of 50 driers. The value of the driers is known as the drying rate or the amount of paper which can be dried per hour, per square foot of drying surface. Applicant has determined, from experiments conducted and data collected in the past, that the drying yrate is equal to the temperature in Fahrenheit degrees multiplied by .0112 minus 1.708. Since the total surface of one 60 inch diameter drier for a trim of one inch is 1.308 square feet, the capacity of a roll in tons per h our equals the drying rate multiplied by 1.308, multiplied by the trim, divided by 2,000,l the number of pounds per ton. The angle of the margin 55 was determined by calculating the number of driers required to dry an equivalent amount of paper at 50 pounds steam pressure and at 25 pounds steam-pressure, the intermediate pressures and number of rolls being in direct proportion. For example, a straight line, as indicated at 62 in Figure 3, starting at 50 driers on the 50 pound circular arc would terminate at 63.4 driers on the 25 pound arc because the ratio based on the comparative drying rate is 1.268 and the same ratio prevails for any other combination. This angular cut is used in lieu of a series of lines, similar to line 62, which would otherwise be required on the scale 2i. The indicia 6-25 'associated with the tons per hours" scale I1 have an index value of one, but the numbers below vsix have been omitted since the range, 6 to 25 tons, represent the extreme limits of production per hour, when the other factors of the scale are considered. The markings in the scale I9, indicating tons per twenty-four hours in hundreds, have a 4proportional value, so that any reading on the scale I9 is twenty-,four . times the corresponding reading on the scale I1. The tonnage produced is the product obtained f by multiplying the implied value, obtained from the scale 2l for the number of driers, by the trim, yindicated on the trim scale I5. This muldicated by the radial lines 22. 'nie muon :or any mm n round in me scala i1 opposite the number in the scale Il for the particular trim under consideration. The product represents the addition of the logarithms of the numbers corresponding to the implied value of the driers and the indicated trim. The production in hundreds of tons per twenty-four oi trim is to 230 inches, corresponding to 1.5 to 2.3 on the logarithmic scale. 'I'he weight scale 59 is a reverse scale, since the speed of travel of the web, indicated by the speed scale I5, is inversely proportionate. It was simpler to make the scale l0 a reverse scale, although, obviously, the opposite arrangement could be adopted, i. e. making the scale I! a reverse scale and the scale 50 a normal one. The index value ofthe scale 50 is 10. but only the portion between 23 and 90 is included, since these gures represent the limits of paper weights in a Fourdrinier kraft board mill of the type with which the embodiment of the invention shown in the accompanying drawings is adapted to be us'ed. The speed scale I5 has an index value of one, but the index is omitted for similar reasons. The scale was developed directly from the scale 2| for the number of driers and the scale 50 for the weight of paper, excluding the production rate scales Il and I9 and the trim scale 45 because the implied tonnage of the scale 2| is on the basis of one drier per one inch trim. This value multiplied by the number of driers, multiplied by the factor 200, divided by the sheet weight gives the speed in feet per minute. The relative positions of the scales I5, Il and 2| on the base I0 are unimportant and have been selected for convenience and for even distribution of the lgures over the base. The scale I9 must be in predetermined relation to the scale Il, since the figures in the scale I9 correspond to a multiple of those in scale I1. In other words, each figure in scale I9 corresponds to the ligure in scale I'I, radially aligned therewith, when multiplied by 24. e 'I'he relation of the scales 45, 50 and 55 to the scales on the base and to each other are of vital importance, once the scales on the base have been positioned in the arbitrarily selected relation to each other. The relative positions of the scales on the slide or disc I2 are determined by working out one or more specific problems, in accordance with the principlesand the formula explained below. When these scales have been so positioned in accordance with one or more specific examples, the gures will be accurate for all other combinations of temperatures, numbers of dryers, speeds of movement, weights of paper, trim and production in tons per hour and hundreds of tons per 24 hours. Obviously, the reverse procedure in laying out the scales could be adopted. That is vto say. the scales could ilrst be marked oi on the disc. and then applied to the base, by plotting the results of one or more mathematical computations. The multiplication and division is mechanically performed simultaneously with the setting of the revolving, disc for ascertaining the tonnage, as explained above. The speed of movement of the sheet is found on the scale I5 opposite the indicia on the scale 50, corresponding t0 the selected sheet weight. Also available, without moving the revolving disc, is the corresponding speed for any sheet weight from 23 to 90 pounds. The efficiency scale on the angular edge 58 of the window 4l is useful because the calculations of the other scales have been predicated upon 100% efficiency in operation and many driers do not come up to this standard. The figures on this scale are spaced apart as in a logarithmic scale and therefore automatically indicate the designated percentages. This logarithmic scale has numerals associated with the percentages indicated thereon. The marking l is located in respect to chart 2l so that it will register initially with the minimum number of driers, which is fifty, when that number of dryers registers with the minimum steam pressure, which is twentylive pounds. When the radial line representing the number of driers selected coincides with the figure 500 in the scale 55, the efficiency is 100%. The figures 90 and 80 are for the purpose of comparing the performance of existing paper machines with the values established for the production calculator. For example, if a machine with sixty driers and 25 pounds steam pressure is producing 6.79 tons of paper per hour for a trim of 150 inches, the 100% emciency gure coincides with the radial line for fifty-four driers and the sixty drier radial line coincides with the 90% eciency figure. Hence, the efficiency is 90%. Also, if the same machine without reference to the tonnage is operating at a Speed of 80 feet per minute for a 3G pound sheet, the drier radial line (100% efficiency) coincides with 80. Therefore, the eiciency is 80%. The equivalent speed for 100% efficiency would be 600 feet. The angular cut, adjacent the eticiency figure, has no particular significance, except that it permits more of the 50 pound circular arc to be visible than would have been the case, had the figures been placed on the periphery of the circle. t is thought that the operation of the calculator of the present invention will be entirely clear to those skilled in the art from a consideration of the foregoing description. For instance, if it is desired to find the production of hours and the speed of movement of the sheet, when the number of driers and steam pressure are known, it is simply necessary to revolve the disc l2 until the line 25a-29a leading from the steam pressure intersects the line 22 corresponding to the number of driers employed. Adjacent to the scale 45 marked trim" will be found the production per hour on the scale il and per tweny-four hours on the scale i9. Adjacent the figure on the weight scale 50 corresponding to the paper being produced will be found, on the speed scale i5, the figure corresponding to the speed of movement of the paper in feet per minute. Conversely, when it is desired to find the number of driers and steam pressure required, when the production in tons and the trim are known, it is necessary simply to revolve the disc until the known production and trim coincide. All possible combinations of numbers of driers and steam pressures are indicated by the points of intersection between the various lines 25a- 29a and the lines 22. If it is desired to find that alternate speeds for various sheet weights, when the speed for a deflnite sheet weight is known, the disc is rotated until figures for the known speed and sheet weight coincide. Opposite any weight on the scale 50 paper in tons per hour or tons per twenty-four will be found the corresponding speed, in the scale IB, ln feet per minute. In a similar manner, it is possible to read from the speed scale back to the weight scale, to determine various weights of paper that may be produced at different speeds, using any particular combination of temperature and number of driers. If it is desired to find the eiiiciency when the production, trim and number of driers are known, the disc should be revolved until the trim and production selected coincide. Adjacent the number of driers actually employed will be found the efficiency in percent. Similarly, the efficiency may be determined. if the sheet weight, speed and number of driers are known. This is accomplished by revolving a disc until the sheet weight and speed coincide. Adjacent the number of driers will be found the efiiciency in percent. As illustrating the simplicity of calculation with the device of the present invention, as compared with mathematical calculations heretofore employed, a typical mathematical calculation will be explained. To obtain the figure for the tons per hour produced, for a known steam pressure, number of driers and trim, it is necessary to calculate the drying rate, as explained above, by multiplying the temperature times .0112, minus 1.708. The drier surface must also be computed, by multiplying the number of driers by 1.308 and multiplying the product by the trim in inches. In order to calculate the tons per hour, the drying rate must be multiplied by the drier surface and the product divided by 2,000 (pounds per ton). As explained above, these complicated calculations may be performed mechanically, by the use of the instrument of the present invention by a simple manipulation of the slide, to bring the steam pressure and number of driers into registration. The production may be read on the scale I l, opposite the figure for the trim in inches. The fundamental equation showing the relationship between various factors involved in this device may be expressed as follows: PSNXSXRX T 2,000 in which P=production in tons per hour, N=the number of dryers, S=l.308 (surface in square feet of one dryer for each inch of trim), R=the drying rate (temperature) (M12-1.708), T=the width of the trimmed sheet in inches, and 2,000 stands for pounds per ton. If we have the problem of determining the production in tons per hour of a paper machine having fifty dryers, each 60 inches in diameter, with fifty pounds steam pressure per square inch therein (temperature 297.7 F.) and 150 inchtrim, the problem would be worked as follows: 50X 1.308X 1.6262X 150 The dliliculties in performing the multiplications and division required in solving this problem are obvious. To solve the same problem by the calculator of the present invention, the fifty pound steam pressure on scale 55 is set to coincide with the 50 dryer ngure in scale 2|. By reading the number in scale H opposite the indicia corresponding to l 50 in the trim scale 4l, the answer is found. Without changing the setting of the disc, the production in 24 hours may be determined, by reading the figure in the scale I9, opposite the |50 trim ilgure. Another formula showing the relation between the speed of movement of the sheet in 100 feet per minute, the weight of the paper, per 1,000 square feet, and the tons per hour and trim in inches may-be expressed as follows: S=speed per minute in 100 feet, 2,000=pounds per ton, K a constant=200 for 1,000 square feet basis, W-:weight of sheet in pounds per square feet, and T=trim in inches. The mathematical calculations required to reduce this formula are somewhat involved, but they may be automatically performed by simply setting one pair of known figures in the problem, whereupon the unknown may be read opposite the third known quantity. For instance, ii' the trim and the paper weight are known, as well as the speed in feet per minute, the production gures per hour or 24 hours may be determined by adjusting the weight and speed gures and reading the production opposite the number trim. Similarly, if a predetermined production schedule must be met, for a known weight and trim of Paper, the speed may be determined by adjusting the production rate (tons per hour) and the trim to correspond, whereupon the speed in 100 feet per minute may be determined by reading the figure in the scale i opposite to the known weight in scale 50. It must be understood that the invention is not limited to the details of construction shown in the accompanying drawings and described above, since the principles of invention may be embodied in many modified forms. All devices coming within the scope of the appended claims and their equivalents are intended to be included. I claim: l. A calculator for solving problems in the manufacture'of paper involving variables relating to rate of production in weight, number of driers. temperature of driers, width of paper and speed of movement oi.' the sheet, having the relation expressed by the formula p N XS X R X T 2,000 in which R=the drying rate (temperature in degrees Fahr-` enheit X.01121.708), T=the width of the trimmed sheet in inches, and 2,000=pounds per ton, said calculator comprising a base having logarithmic scales arranged on arcs of progressively larger concentric circles, the innermost scale corresponding to numbers of driers, the next outer scale corresponding to speeds of movement of the sheet. and the outermost scale corresponding to rates of production in tons per unit of time, and a slide mounted for rotation on the center of said concentric circles and having margins registering with the scales on the base and logarithmic scales along said margins corresponding respectively with the temperatures or steam pressures of the rolls, the weights of the paper and the trim of the paper, the scales being so arranged that, for a setting of any one pair of variables represented by a scale on the base and the adjacent scale on the slide, a plurality of other corresponding pairs oi variables are indicated in the two other sets of scales on the base and slide, respectively, the slide having a lgenerally arcuate opening therein, exposing the in nermost, number oi.' driers. scale on the base, said opening being dened at one end by a straight line margin disposed at an oblique angle to a radius of the slide, the temperature or steam pressure scale being arranged along said straight line margin in position to register with the number of driers scale therebelow. 2. A calculator for solving problems in the manufacture of paper involving variables relating to rate of production in weight, number of driers, temperature of driers, width of paper and speed of movement of the sheet, having the relation expressed by the formula in which P=production in tons per hour, N=the number of driers, S=.1308 (surface in square feet of each 60 inch drier for each inch of trim), R=the drying rate (temperature in degrees Fahrenheitx .M12-1.708), T=the width of the trimmed sheet in inches, and 2,000=pounds per ton, said calculator comprising a base having logarithmic scales arranged on arcs of progressively larger concentric circles, the innermost scale corresponding to numbers of driers, the next outer scale corresponding to speeds of movement of the sheet, and the outermost scale corresponding to rates of production in tons per unit of time, and a slide mounted for rotation on the center of said concentric circles and having margins registering with the scales on the base and logarithmic scales along said margins corresponding respectively with the temperatures or steam pressures of the rolls, the weights of the paper and the trim of the paper, the scales being so arranged that, for a setting of any one pair of variables represented by a scale on the base and the adjacent scale on the slide, a plurality of other corresponding pairs of variables are indicated in the two other sets of scales on the base and slide, respectively, the slide having a generally arcuate opening therein exposing the innermost number of driers scale on the base, the scale for temperature or steam pressure being arranged along a margin of said opening in position to register with the number of driers scale therebelow. 3. A calculator for solving problems in the manufacture of paper involving variables relating to rate of production in weight, number of driers, temperature of driers, width of paper and speed of movement of the sheet, having the relation expressed by the formula P: NX S X RX T 2,000 in which P=production in tons per hour, N :the number of driers, 82.1308 (surface in square feet of each 60 inch drier for each inch of trim), R=the drying rate (temperature in degrees Fahrenheit .01121.708) T=the width of the trimmed sheet in inches, and 2,000=pounds per ton, said calculator comprising a base having logarithmic scales arranged on arcs of'progressively larger concentric circles, the innermost scale corresponding to numbers of driers, the next outer scale corresponding to speeds of movement oi the sheet, and the outermost scale corresponding to rates of production in tons per unit of time, and a slide mounted for rotation on the center of said concentric circles and having margins registering with the scales on the base and logarithmic scales along said margins corresponding respectively With the temperatures or steam pressures of the rolls, the weights of the paper and the trim of the paper, the scales being so arranged that, for a setting of any one pair of variables represented by a scale on the base and the adjacent scale on the slide, a plurality ot other corresponding pairs ot variables are indicated in the two other sets of scales on the base and slide, respectively, the slide having a generally arcuate opening therein exposing the innermost number of driers scale on the base, the scale for temperature or steam pressure being arranged along a margin of said opening in position to register with the number of driers scale therebelow, the slide having other outer margins disposed on arcs of concentric circles, with the weight scale along the margin of less radius in position to register with the speed of movement scale, and the trim scale along the margin of greater radius in position to register with the rate of production scale HARVEY G. MCDOWELL. Referenced by
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