US2506390A - Percentage computation aid - Google Patents

Description

May 2, wg@ J. R. SEARS 506,390

PERCENTAGE COMPUTATION AID'- APPARATUS Filed Jan. 27, 1947 5 Sheets-Sheet l EH (y Gttorneg S May 2, i950 J. n. SEARS 2,5@'gn`;

PERCENTAGE COMPUTATION AID APPARATUS Filed Jan. 27, 1947 5 sheetS-shet 2 i@ Llull.

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Mayv 2, 1950 J. R. SEARS 295%939@ PERCENTAGE COMPUTATION AID APPARATUS Filed Jan. 27,1947 5 Sheets-Shree?, 5

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bte/magg Maf; 2, 1950 J. R. SEARS PERGENTGE COMPUTATION AID APPARATUS 5 Sheets-Sheet Filed Janv. 27, 1947 Syvum/MM @Him/AWS `N b N MN BNN May 2, 1950 J. R. SEARS PERCENTAGE COMPUTATION AID APPARATUS 5 Sheets-Sheet 5 Filed Jan. 27, 1947 @w @m y abbo/MMS Patented May 2, 1950 PERCENTAGE ooMPU'rATIoN AID ArPARATUs John 1i... Scars, N Orfolk, Va. .application January 27, 1947, Serial No. 724,616 13 Claims. (C1. 5235-787) This invention relates to percentage aid coinputation apparatus, and more particularly to apparatus for co-relatively positioning` tables or columns of numerical values in such manner that percentages of principal values at varying percent rates may easily be determined. The invention may be embodied in apparatus of the general class referred to in which percentages are tabulated in columns on rotatable drums or cylinders.

An objects of the invention is to provide an apparatus of the character stated which, for a given capacity as to the range oi computations, is more compact than apparatus previously provided for the same use. In attaining this object, I provide, in general, two apparatus groups or sections for determining percentages of primary and secondary parts of a principal value, based on a selected percent rate, together with means or markings for co-relating the thus determined percentages and rendering them corelatively readable and distinguishable from percentages oi the principal sum based on other and non-selected percent rates.

Another object of the invention is to provide a percentage computation aid apparatus including two coaxial, rotatable cylinders mounted to rotate independently of each other without any tendency of one cylinder to rotate the other cylinder.

Another object of the invention is to provide apparatus of the kind referred to including a simple and electve arrangement for mounting bands or rings marked with percentage values on a cylinder or drum.

Other objects will become apparent from a reading of the following description, the appended claims, and the accompanying drawings, in which:

Figure 1 is a front elevational View of a simple form of apparatus embodying the invention;

Figure 2 is a longitudinal sectional view of the apparatus shown in Figure l, but with some parts omitted;

Figure 3 is a detail end elevational view of a cylinder and band, illustrating the arrangement for maintaining the band in a predetermined circumferential setting or position on the cylinder;

Figure 4 is a detail View showing a group of alternative percent rate markings which may be used in place of percent rate markings shown in Figure 1;

Figure 5 is a perspective view illustrating a casing or housing for enclosing apparatus of the kind shown in Figures l to 4;

Figure 6 is a iront elevational view of a modified embodiment of the inventionj Figure 7 is a fragmentary vertical section on the line 'I 'I of Figure 6; and

Figure 8 is a fragmentary section on the line 3-8 oi Figure 7.

Figures l to 3 inclusive illustrate a simple and preferred iorm or" apparatus adapted to be used as an aid in computing percentages, particularly for computing` interest in banks, building loan association oces, and other establishments in which interest on diiierent principal amounts and at different interest rates has to be computed as part oi the daily work.

The apparatus shown in Figures l to 3, considered in its general nature, includes a support or stand A on which are mounted two independently rotatable cylinder member B and B disposed with their inner ends in face-to-face relationship behind an opaque shield generally designated C fixed to the support A by a bracket l. The shield C is shown as comprising a single structural part, but considered functionally it comprises two inclicating sections,v one designated 2 between the vertical center line of the apparatus and the left end of the shield, and the other designated between the vertical center line and the right end of the shield as viewed in Figure l.

The shield indicating section 2 is formed with a principal value designation part 3 iormed with a window #3, and is provided with a series of horizontally aligned percent rate markings 5, 6, 7, 8, 9, and 19. The procent rate markings may be changed according to the computations to be made. The markings shown in Figure l are respectively in descending progression 6%, 51/2%, 5%, l1/2%, 4%, and 3%. rEhe shield indicating section E! is similar to the indicating section 2 and includes a primary value designation part 3 formed with a window b3', as well as percent rate markings 5', 6', 7', 8', 9', and l0 which are the saine as to value and progression as the percent rate markings 5 to 10 inclu ive on the section i?.

The cylinder B is provided with an column l! of primary principal value indicia located at the left end ci the cylinder so to be behind the 'principal value designation 3 of the shield section 2. The calumn il is ii th principal values increased 1G@ units between each two adjacent value indicia up to ten thousand. The lcylinder B also is provided with annular columns l2, i3, i4, i5, .1.- primary percentage indicia. These columns are on the cylinder B to be disposed behind the percent rate markings 5, G, 7,8, 9, and l0 on the shield 'section 2. is formed with a plurality oi 20, 2 l, 22, and 23 arranged in stepped relationship with the respective view openings being disposed directly under, that is aligned transversely with the respective percent rate markings 5, 6, 7, 8, 9, and l0.

The cylinder B can be rotated by means of a knob device 24 attached to the cylinder in a manner to be described hereinafter. By rotating the cylinder, any selected principal value in the column l l can be made to register with the window 4. The primary percentages listed in the columns l2, i3, i4, l5, i6, and il are such that when a selected principal value registers with the opening 4 the correct percentage will be displayed in the view opening directly below the percent rate marking used in the computation. For example, if it is desired to determine the interest on $8,600 at 6% for one month, the cylinder B is turned until the principal value $8,600 registers with the window 4, and the percentage or interest displayed through the view opening l directly under the 6% marking 5 is seen to be $43.00. If it is desired to iind the interest on $8,600 for one month at 51/2%, the reading of the interest is made through the view opening I9 directly under the 51/2% marking 6, and is found to be $39.42. Similarly, the interest or percentage at the rates shown in the markings 7, 8, 9, and 10 can be read easily through the openings 20, 2|, 22, and 23, respectively.

The cylinder B' is provided or marked with an annular column il of secondary principal value indicia increasing by ones or units up to $100. The cylinder B' also is marked or provided with annular columns of percentage indicia designated 12', 13', 14', 15', 16', and 17' disposed respectively behind the percent rate markings 5', 6', 7', 8', 9', and l0. The shield section 2 is formed with stepped view openings i8', I9', 20', 2|', 22', and 23' respectively aligned directly under the percent rate markings 5', 6', 7', 8', 9', and The view openings in the shield indicating section 2' are arranged in stepped relationship similarly to the view openings in the shield section 2, that is, the uppermost opening I8' in the shield section 2' is aligned horizontally with the uppermost opening I8 in the shield section 2, and both openings I8 and I8' are disposed under the 6% markings. Similarly, the immediately lower openings i9 and IS are horizontally aligned with each other, and are disposed under the 51/2% sign markings, and so on. The percentage columns l2 to Il inclusive are so constituted that when the cylinder B' has been turned by means of a knob device 2li to bring a selected secondary principal value into registration with the window 4', the percentage sought will be found displayed in the view opening disposed under the marking displaying the percent rate use in the computation. Thus, if it is desired to nd the interest on a secondary principal value of $44 for one month at"6%, the cylinder B' is rotated to bring the value $44 in the column Il' into registration with the window Il'. The interest will be observed in the view opening I8' aligned with the six percent sign marking 5', and will be seen to be $0.22.

One of the advantages of a construction embodying the invention and including the two cylinders B and B in combination with the two shield sections 2 and 2 marked as described above is that the apparatus can be built comp-actly to occupy a small space and still have the capacity for computing percentages at varying rates on a large number of principal values. Thus, in the '(5 form shown, the cylinders need be of a diameter only great enough to permit the inclusion of onehundred items in each column, which does not require a cylinder of great circumference, but still permits the nding of percentages on values varying by ones up to ten thousand. For example, in nding the interest on $8,644, for one month at 6%, the cylinder B would be set to cause the primary principal value $8,600 to register with the window 4, and the interest on the primary value would be observed through the view opening i8 as being $43.00. rIhen the cylinder B would be positioned tocause the secondary value $44 to register with the opening 4', and the secondary interest would be observed through the window i6' as being $0.22. By a simple addition, the interest on the whole sum of $8,644 would be determined as $43.22. It is apparent that if the two cylinders B and B' and the associated shield sections were not used in combination, only a single cylinder and shield section being employed, it would be necessary for the columns on the single cylinder to include ten thousand items, requiring a very large circumference and prohibitively large apparatus.

In accordance with a further feature of the invention, the shield C is provided, formed, or marked to facilitate the reading of the related primary and secondary percentages in the proper View openings. In the form shown in Figure l, the shield C is marked with guide lines 20, 26, 2l, 26, 29, and 30 which extend respectively between and denote horizontally aligned pairs of view openings in the respective shield sections 2 and 2'. Thus, the guide line 25 extends between the horizontally aligned view openings i3 and i6', both of which are disposed under the 6% markings; the guide line 26 extends between the view openings i0 and i9' both of which are disposed under the 515% markings; and so on. In finding both the primary `and secondary percentages of a given number, say $8,644, the cylinders B and B' are positioned as previously explained and the primary percentage-$43.00-is read through the opening i3 under the 6% marking; but instead or locating the secondary opening i3' by reference to the percent marking 5' above it, the operator's eye follows across the guide line 25, which visually pairs the opening l0 with the opening i8. The guide line 25 serves in a sense to couple the openings i3 and l0' which are associated respectively with the primary and secondary percentages under similar percent rate markings. In the same way, the guide lines 26, 2, 23, 29, and 30 visually couple other associated pairs o1 view openings so as to facilitate substantially simultaneous reading oi related primary and secondary percentages determined at equal percent rates.

In using the apparatus, it is desirable to operate both cylinders from one side, usually the left side, in order that the operators right hand may be free for making written notes. The apparatus shown in Figures 1 and 2 is so constructed as to provide this advantage and the particular construction is such that it provides the further advantage that turning of either of the cylinders B-B' will not tend to turn the other cylinder and move it from its previous setting. In other words, the arrangement is such that if the cylinder B is rst set to cause a selected principal value to be displayed through the window il, the cylinder B' may be turned thereafter to cause a selected secondary principal value to register with the window 4' without producing any tendency yto turn or drag the cylinder B from its previously set position. For obtaining these desirable advantages, the cylinders B and B are mounted on the support A by a novel construction shown in Figure 2. This construction includes a hub 3l which is integral with the support A and is bored to receive a sleeve 32, the opposite ends of which protrude from the hub 3l yand provide bearing portions shown at 33 and 33. The sleeve may be locked or secured in xed relationship to the hub 3l by any suitable means, for example, by set screws 34-34. The cylinders B and B are formed with hubs 35 and 35 journalled respectively on the bearing portions 33 and 33', so that the cylinders are mounted independently on the sleeve 32 and do not touch each other. The knob 2d for turning the cylinder B is secured to the outer and left hand end of the cylinder B by any suitable means, such as screws 36. The knob 2st for turning the cylinder B is, as stated before, located at the same side of the apparatus as the knob 2li. In order to connect the knob 2d' with the cylinder B without causing contacting of any parts which would cause one cylinder to tend to follow the other in rotation, the knob 24 is formed with an axial opening 3l into which extends, with ample clearance, a shank 33 on the knob 24. The shank 38 is screwed to the which extends through the sleeve 32, the knob 24 being locked to the rod 39 by means of a screw 49. The right end of the rod 39 is attached by a screw 4l to a non-circular part 42 fitted in a similarly shaped recess 43 in the cylinder B.

It will be seen that the group of parts comprising the knob 24', the rod 39, and the cylinder B has no operative or contacting connection with the group of parts comprising the knob 24; and the cylinder B. There is positive clearance between the groups ci parts, and consequently either knob and the parts connected to it can be turned to rotate the associated cylinder without producing any tendency to rotate the other cylinder.

Preferably, the percent rate markings 5 to 10 inclusive and 5 to 10 inclusive are interchangeable with other percent rate markings, according to the computations to be made. The markings may be changed in any desired manner, as for example, by using replaceable or interchangeable tabs or labels or by writing in different percent rates. Figure 4 shows a Set of percent rates which could be substituted for those shown in Figure 1. The percent rates shown in Figure 4 are all based on six percent but they progress according to the number of months for which interest is to be computed.

When a dinerent set or series of percent rate markings used, it usually will be necessary to change the columns of percentages 12 to 17 inclusive and 12 to 17" inclusive. In order that this change may be made readily, the columns of percentage values preferably are marked on removable rings or bands 44 (see. Figure 3) adapted to be slipped on and on the cylinders B and B in an axial direction. Similarly replaceable bands or rings 44 marked with difiere-nt columns of principal values may be employed. The bands or the cylinders, or both are provided with means for maintaining the bands in predeterminedr positions circumferentially with respect to the cylinders. In the constructionv shown in Figure 3, the bands vare formed with internal corrugations i5 adapted to mate with similarly formed corrugations 46 on the cylinder- B. Thecylinder B may be formed with, similar corrugationsadapted to left end of a rod 3S' with the cylindersv B and B mate with internal corrugations of the associated bands.

Figures l to 4 show a percentage computation aid apparatus of simple form comprising a minimum number of parts. The construction described may easily be mounted in a casing or housing D as shown in Figure 5. Only a few reference characters have been applied to Figure 5 to indicate generally parts which correspond to parts of the construction shown in Figures 1 to 4 inclusive.

In order that the cylinders B and B may be held against axial shifting on the sleeve 32, means are provided for coupling the cylinders to the hub 3l of the standard A. The hub 35 of the cylinder B is formed with a groove 41 adjacent its tapering inner end portion 43. The groove 4l receives a stud 49 carried by a spring nger 5d secured to the hub 3| by a screw 5l. When the parts are in the assembled relationship shown in Figure 2, the stud 49 cooperates with the sides of the groove 4? to maintain the cylinder Bgagainst axial shifting. However, the cylinder B may be removed by forcing it axially toward the left, which will cause the spring finger 50 to yield, permitting the stud 4S to rise out of the groove 41 and allow the cyliner hub 35 to move axially to the left. When the cylinder B is to be set in its operative position, it is placed on the sleeve 32 and pushed to the right, causing the tapered edge 4S to lift the stud 49 against the urge or the spring iinger 5l). Upon further movement of the cylinder B, the stud 49 will drop into place in the groove 47. Similarly, the hum 35 of the cylinder B' is formed with a groove 41 which receives a stud 49 carried by a spring finger 56 secured to the hub 3l by a screw 5 l Figures 6 to 8 illustrate a modified embodiment of the apparatus including a movably mounted opaque screen E adapted to be set in diierent positions for obstructing or cutting off view through the openings lt to 23 inclusive and i8 to 23' inclusive, with the exception of two selected horizontally aligned View openings related to equal percent rate markings. Broadly considered, the movable screen aids in the reading of primary and secondary percentages in much the same manner as the guide lines 25 to 9i) inclusive shown in Figure l. Consequently, the guide lines may be omittedfrom the shield C in the construction shown in Figures 6 to 8. The shield C shown in the modication differs from that shown in Figure 1 also in that it is provided with a slot 52 and an additional bracket 53 for assisting the bracket i in. supporting the shield on the standard A. Otherwise the parts shown in Figures 6 to 8 inclusive, with the exception of the screen E and the parts which mount it, are the same as parts shown in Figures 1 to 3 inclusive and are designated by corresponding reference characters.

The screen E is shaped to conform to the surface of a cylinder and is mounted concentrically and the shield C. The screen may be mounted either inside or outside of the shield C, since in either case, the screen can obstruct the view of percentage values on the cylinders B and B. In the form shown, the screen E' is disposed between the cylinders B-B' and the shield C, that is, the screen E is mounted behind the shield C.

The screen is provided with twofmounting arms 54v and 55 which merge at inner ends with a ilat hub 56v snugly mounted in a slot 5'! formed in 'thel hub Y3l of the standard A. The at hub 56 is journalled on the ixed sleeve 32 and has its opposed ilat surfaces crimped or otherwise formed or equipped to provide for frictional engagement of the hub faces with the sides of the slot l to hold the screen E frictionally but releasably in set position. The screen E is rockable about the sleeve 32, and in order that it may move high enough, it is formed with a slot 58 through which the shield mounting bracket 53 extends. A button 59, secured to the screen E and extending freely through the slot 52 in the shield C, provides for convenient manual raising and lowering lof the screen.

For rendering two selected horizontally aligned view openings in the shield C co-relatively functional, the screen E is formed with two elongated horizontal slots 60 and Se', which in eiect constitute a single slot means extending substantially across the screen. When it is desired to determine the percentage of say $8,644 at six percent ior one month, the knobs 24 and 24 are operated to turn the drums B and B until the primary Secondary principal values $8,600 and $44 register respectively with the windows il and in the shield C. Then the button 59 is moved to rock the screen E to a position in which the slots Et and 60' are disposed directly under the view openings l8 and I8'. The primary and secondary percentages will then appear respectively in the I,

Windows i8 and I8 as $43.00, and $0.22. With the screen E positioned as described, the opaque portion of the screen, that is the part of the screen other than the slots 60 and 50', will obstruct view through the openings i9 to 23 and I9 or 23' so that the only percentages viewable through the shield C and screen E are those determined at the 6% rate which are to be found.

If it should be desired to iind the percentage or interest on $8,644 for one month at five and one half percent, the screen is removed downwardly to cause the slots 60 and Gi to register with the view openings i9 and I9', all the other view openings then being cut oi or rendered noniunctional. By shifting the screen E to other positions, the primary and secondary percentages can readily be determined on the basis of any selected interest rate.

The constructions illustrated by way of example embody the invention in preferred forms but it will be understood that changes may be made without departing from the invention as defined in the claims.

I claim:

l. In a percentage computation aid apparatus, a support; a relatively ilxed shield having two indicating sections; a first rotatable member provided with indicia, individual items of which each represents a primary part of a principal value and are adap-ted to be denoted selectively by one of said indicating sections according to the rotated position of said member; a second rotatable member provided with indicia, individual items of which each represents the secondary part of a principal value and are adapted to be denoted selectively by the other of said indicating sections according to the rotated position of said second member; means mounting said rotatable members on said support independently of each other with their inner ends in mutual face-to-face relationship for rotation about a common axis and with each of said members being free to rotate without tending to rotate the other of said members; a first manually operable device connected to the cuter end of one of said members for rotating it a second manually operable device at the same end of said one of said members; means operatively connecting said second manually operable device to the other of said members for rotating it, said second manually operable device and said connecting means being free of connection to said first manually operable device and said one of said members, whereby either manually operable device may be operated to rotate the member connected thereto without producing any tendency to rotate the other member, and means cooperating with the respective indicating sections of said shield to facilitate the collective relating of selected markings on the two cooperating members.

2. In a percentage computation aid apparatus, a support; a relatively xed shield having two indicating sections; a first rotatable member provided with indicia, individual items of which each represents a primary part of a principal value and are adapted to be denoted selectively by one of said indicating sections according to the rotated position of said member; a second rotatable member provided with indicia, individual items of which each represents the secondary part of a principal value and are adapted to be denoted selectively by the other of said indicating sections according to the rotated position of said second member; a sleeve carried by said support and having end portions protruding oppositely from said support to provide axially spaced bearing portions on which said members are journalled respectively with their inner ends in face-to-face relationship; a rst manually operable device connected to the outer end of one of said members for turning it and having an axial opening coaxial with said sleeve; a rod connected to the outer end of the other of said members and extending through said sleeve and said opening; a second manually operable device on said rod and adjacent said first manually operable device, said second manually operable device, said rod, and the one of said members to which the rod is connected being completely free of connection to said i'lrst manually operable device and the member to which it is connected, and means cooperating with the respective indicating sections of said shield to facilitate the collective relating of selected markings on the two cooperating members.

3. In a percentage computation aid apparatus, a support; a relatively xed shield having two indicating sections; a first rotatable member provided with indicia, individual items oi which each represents a primary part of a principal value and are adapted to be denoted selectively by one of said indicating sections according to the rotated position of said members; a second rotatable member provided with indicia, individual items of which each represents the secondary part of a principal value and are adapted to be denoted selectively by the other of said indicating sections according to the rotated position of said second member; a sleeve carried by said support and having end portions protruding oppositely from said support to provide axially spaced bearing portions on which said members are journalled respectively with their inner ends in face-to-face relationship; a rst operating knob secured to the outer end of one of said members and having an axial opening coaxial with said sleeve; a rod secured to the outer end of the other of said members and extending through said sleeve and into said opening; la second operating knob secured to said rod and being located adjacent said rst operating knob, there being positive clearance between the group of parts including said iirst operating knob and the associated rotatable member and the group of parts comprising said second operating device, said rod, and the associated rotatable member, and means cooperating with the respective indicating sections of said shield to facilitate the collective relating of selected markings on the two cooperating members.

4. In a percentage computation aid apparatus, a shield comprising two adjacent indicating sections, each section being marked with a series of progressively varying percent rates and having a principal value designation part and a series of individual view openings aligned respectively with the percent rate markings, said openings being in step arrangement, the percent rate markings on said two sections being the same as to values and progression and the step arrangement of the view openings in said two sections being similar; guide lines on said shield extending respectively between and denoting two View openings in the respective sections aligned with equal percent rate markings; a iirst member mounted to move behind one of said indicating sections and being marked with a column of primary principal values adapted to register with the principal value designation part of said one of said indicating sections, and being also marked with columns of primary percentages of said primary principal values adapted to be displayed through the openings aligned with the percent rate markings on said one of said shield sections; and a second member mounted to move behind the other of said indicating sections and being marked with a column of secondary principal values and being also marked with columns of secondary percentages of said secondary principal values adapted to be displayed through the openings aligned with the percent rate markings on said other of said indicating sections.

5. In a percentage computation aid apparatus, a shield comprising two adjacent indicating sections, each section being marked with a series of aligned progressively varying percent rates and having a principal value designation part and a series oi individual view openings aligned respectively with the percent rate markings transversely to the alignment of the markings of said series, said openings being in step arrangement and at progressively varying distances from the percent rate markings with which they are respectively aligned, the percent rate markings on said two sections being the same as to values and progression and the step arrangement of the View openings in said two sections being similar; guide lines on said shield extending respectively between and denoting two view openings in the respective sections aligned with equal percent rate markings; a first member mounted to move behind one of said indicating sections and being marked with a column of primary principal values adapted to register with the principal value designation part of said one of said indicating sections, and being also marl-ed with columns of primary percentages of said primary principal values adapted to be displayed through the openings aligned with the percent rate markings on said one or said shield sections; and a second member mounted to move behind the other of said indicating sections and being marked with a column of secondary principal values and being also marked with columns of secondary percentages oi said secondary principal values adapted to be displayed through the openings aligned with the percent rate markings on said other of said indicating sections, all of said columns extending transversely to said series of aligned percent rates.

6. In a percentage computation aid apparatus, a shield comprising two adjacent indicating sections, each section being marked with a series of progressively varying percent rates and having a principal value designation part and a series of individual view openings aligned respectively with the percent rate markings, said openings being in step arrangement, the percent rate markings on said two sections being the same as to values and progression and the step arrangement of the View openings in said two sections being similar; guide lines on said shield extending respectively between and denoting two view openings in the respective sections aligned with equal percent rate markings; a nrst cylinder mounted to rotate behind one of said indicating sections and being marked with a circumferential column of primary principal values adapted to register with the principal value designation part of said one of said indicating sections, and being also marked with circumferential columns of primary percentages of said primary principal values adapted to be displayed through the openings aligned with the percent rate markings on said one of said shield sections; and a second cylinder mounted coaxially with said rst cylinder to rotate independently oi said rst cylinder and behind the other of said indicating sections and being marked with a circumferential column of secondary principal values and being also marked with circumferential columns of secondary percentages of said secondary principal values adapted to be displayed through the openings aligned with the percent rate markings on said other of said indicating sections.

'7. In a percentage computation aid apparatus, a cylinder provided with a circumferential column of principal value markings; a series of separate annular sleeves mounted coaxially on said cylinder in end to end relation and being respectively marked with percentages, said annular sleeves being mountable on and demountable from said cylinder by movement axially of the cylinder; and cooperating means on the cylinder and sleeves respectively for maintaining said sleeves in predetermined position circumferentially with respect to said cylinder.

8. In a percentage computation aid apparatus, a cylinder provided with a circumferential column of principal value markings; a series of separate annular sleeves mounted on said cylinder and being respectively marked with percentages, said annular sleeves being mountable on and demountable from said cylinder by movement axially of the cylinder; and inter-engaging corrugations in the cylinder and sleeves respectively for maintaining said sleeves in predetermined position circumierentially with respect to said cylinder.

9. In a percentage computation aid apparatus, a fixed shield comprising two adjacent indicating sections each marked with a series of progressively varying percent rates and having a principal value designation part and a series of view openings aligned respectively with the percent rate markings, said openings being in step arrangement, the percent rate markings on said two sections being the same as to values and progression and the step arrangement of the view openings in said two sections being similar; a rst member mounted to move behind one of said indicating sections and being marked with a column of primary principal values adapted to register with the principal value designation part of said one of said indicating sections, and being also marked With columns of primary percentages of said primary principal values adapted to be displayed through the openings aligned with the percent rate markings on said one of said shield sections; a second member mounted to move behind the other of said indicating sections and being marked with a column of secondary principal valuesY and being also marked with columns of secondary percentages of said secondary principal values adapted to be displayed through the openings aligned with the percent rate markings on said other of said indicating sections; and a screen mounted in iront of said movable members to move in the same general direction as said movable members move, said screen having slot means extending transversely to said columns and being adapted to register simultaneously with two selected view openings in the respective indicating sections aligned with equal percent rate markings, the non-slotted portion of said screen cutting off the view through the open openings of the percentage Value columns behind said other openings.

10. In a percentage computation aid apparatus, a xed shield comprising two adjacent indicating sections each marked with a series of aligned progressively varying percent rates and having a principal value designation part and a series of view openings aligned respectively with the percent rate markings transversely to the Valignment of the markings of said series, said openings being in step arrangement and at progressively varying distances from the percent rate markings with which they are respectively aligned, the percent rate markings on said two sections being the same as to values and progression and the step arrangement of the view openings in said two sections being similar; a rst member mounted to move behind one of said indicating sections and being marked with a co1- umn ci primary principal values adapted to register with the principal value designation part of said one of said indicating sections, and being also marked with columns of primarypercentages of said primary principal values adapted to be displayed through the openings aligned with the percent rate markings on said one of said shield sections; a second member mounted to move behind the other of said indicating sections and being marked with a column of secondary principal values and being also marked with columns of secondary percentages of said secondary principal values adapted to be displayed through the openings aligned with the percent rate markings on said other of said indicating sections; and a screen mounted in front of said movable members to move in the same general direction as said movable members move, said screen having slot means extending transversely to said cohunns and beingV adapted to register simultaneously with two selected view openings in the respective indicating sections aligned with equal percent rate markings, the non-slotted portion of said screen cutting oir the View through the other openings of the percentage value columns behind said other openings, all of said columns extending transversely to said series of aligned percent rates.

Y Vl1. In a percentage computation aid apparatus,

Va xed shield comprising two'adjacent indicating sections each marked with a series of progressively varying percent rates and having a principal value designation part and a series of view openings aligned respectively with the percent rate markings, said openings being in step arrangement, the percent rate markings on said two sections being the same as to values and progression and the step arrangement of the view openings in said two sections being similar; a iirst cylinder mounted to rotate behind one of said indicating sections and being marked with a circumferential column of primary principal values adapted to register with the principal value designation part of said one of said indicating sections, and being also marked with circumferential columns of primary percentages of said primary principal values adapted to be displayed through the openings aligned with the percent rate markings on said one of said shield sections; a second cylinder mounted coaxially with said rst cylinder to rotate independently of said first cylinder and behind the other of said indicating sections and being marked with a circumferential column of secondary principal values and being also marked with circumferential columns of secondary percentages of said secondary principal values adapted to be displayed through the openings aligned with the percent rate markings on said other of said indicating sections; and a screen mounted in front of said cylinders to move in the same general direction as said cylinders move, said screen having slot means extending transversely to said columns and being adapted to register simultaneously with two selected view openings in the respective indicating sections aligned with equal percent rate markings, the non-slotted portion of said screen cutting oi the View through the other openings of the percentage value columns behind said other openings.

12. In a percentage computation aid apparatus, a centrally disposed support; a transverse mounting member carried by said support and protruding therefrom to form oppositely disposed, coaxial bearing members; a primary principal value and percentage computation unit rotatably mounted on one of said bearing members; a secondary principal value and percentage computation unit rotatably mounted on the opposite bearing member, independently of said first unit; each of said units comprising a cylinder, marked with a circumferential column to represent parts of principal values and adapted to be combined with markings of the corresponding columns of the opposite unit to collectively constitute selected principal values, and a series of circumferential columns representing percentages of the respective parts of the principal values and adapted to be combined with corresponding columns of the opposite unit to collectively constitute complete percentages of selected principal values; a common shield carried by said support and overlying adjacent portions of the peripheries of said units; said shield comprising two adjacent indicating sections, each marked with a series of aligned progressively varying percentage rates and having a principal value designation part and a series of individual view openings aligned respectively with the percentage rate markings transversely to the alignment of the markings of series, said openings being in step arrangement and at progressively varying distances from the percentage rate markings with which they are respectively aligned; and guide lines on said shield extending respectively between and de- 13 noting two view openings in the respective sections aligned with equal percentage rate markings to facilitate the collective relating of markings of the two cooperating units.

13. In a percentage computation aid apparatus, a iixed shield comprising two adjacent indicating sections each marked with a series of progressively varying percent rates and having a principal value designation part and a series of view openings aligned respectively with the percent rate markings, said openings being in step arrangement, the percent rate markings on said two sections being the same as to values and progression and the step arrangement of the view openings in said two sections being similar; a rst member mounted to move behind one of said indicating sections and being marked with a column of primary principal values adapted to register with the principal value designation part of said one of said indicating sections, and being also marked with columns of primary percentages of said primary principal values adapted to be displayed through the openings aligned with the percent rate markings on said one of said shield sections; a second member mounted to move behind the other of said indicating sections and being marked with a column of secondary principal values and being also marked with columns of secondary percentages of said secondary principal values adapted to be displayed through the openings aligned with the percent rate markings on said other of said indicating sections; a screen mounted in front of said movable members to move in the same general direction as said movable members move, said screen having slot means extending transversely to said columns and being adapted `to register simultaneously with two selected view openings in the respective indicating sections aligned with equal percent rate markings, the non-slotted portion of said screen cutting off the View through the open openings of the percentage value columns behind said other openings, a peripheral slot in said shield, and a radially projecting button on said screen, extending through said slot for manipulating said screen.

JOHN R. SEARS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 675,341 Rice May 28, 1901 698,141 Roegner Apr. 22, 1902 760,360 Wiley May 17, 1904 896,710 Burhans Aug. 25, 1908 914,439 Meilicke Mar. 9, 1909 1,127,492 Musgrove Feb. 9, 1915 1,360,726 Crook Nov. 30, 1920 FOREIGN PATENTS Number Country Date 25,345 Great Britain 1912 40,982 Denmark Oct. 28. 1929

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