Patent GB-840764-A (GB)
Title: Improvements in or relating to data checking apparatus
Inventor: KEEN ALBERT JOHN
IPC: G06F11/10
Filed: 1955-09-13
Abstract: 840,764. Electric check symbol calculating apparatus. INTERNATIONAL COMPUTERS & TABULATORS Ltd. Sept. 7,1956 [Sept. 13, 1955], No. 26166/55. Class 106 (1). Data transmitted from a keyboard, via a data store to the selector magnets of a record card punch is checked by being associated with previously calculated check digits, calculating circuits being provided which receive the data as it is transferred digit-by-digit from the store to the punch magnets and which work out the check digits again for comparison with those previously calculated. As a simple illustration suppose that the data consists of a number, say 673, the check digits 06 are also entered into the store, the value 06 being the residue (modulo 13) (i.e. the remainder after division by 13) of the number 673 multiplied by 960. Multiplication by 960 is to facilitate calculations in money amounts, there being 960 farthings in a pound. The number and its check digits are entered into store and are read-out serially: 673,06, highest significance digit first, to the punch magnets and simultaneously to the check digit calculating circuit. Since the denominational significance of the first digit 6 is not known it is treated as the units digit. The calculating circuit, which consists merely of a conversion network using relay contacts and diodes, produces the residue (mod. 13) of 6 Î 960, that is 1. This value is multiplied by ten to derive the check digit for sixty so that when the next digit, 7, arrives its residue can be added to produce a correct residue for 67. The digit 7 gives a residue of twelve which added to the ten resulting from the previous digit to derive 22. The residue of this, i.e. nine, is multiplied by ten as before and the residue of ninety, i.e. twelve, is stored. The next digit, 3, gives a residue of seven which added to the twelve in store gives nineteen, i.e. a residue of six. This, multiplied by ten, gives a residue of eight, which is stored. The check digits are entered in such a way that the residue of their value times ten is effectively subtracted from the stored value and the result should be zero. The calculating circuit is accordingly modified to enter a complementary residue. The first check digit, O, is now entered producing zero residue, so that the eight is merely multiplied by ten and the residue, two, is stored. The second check digit, 6, gives a complementary residue of eleven which when added to the two in store gives thirteen, the residue (mod. 13) of which is zero. This result shows that the previouslycalculated check digit and those worked out as the number is punched digit-by-digit are identical and that the number has been correctly transmitted. Alphabetic characters.-The invention is concerned with the checking of alphabetic or alphanumeric items. Since alphabetic characters are represented on the punched cards by two perforations, one in the 1-9 positions and one in a zone position O, X or Y, they can conveniently be converted to a numerical equivalent by allotting the zone positions values 10, 20 and 30. Letter " A " which is represented by perforations in positions " 1 " and " Y " has an equivalent of 31. According to the invention check digits are calculated by dividing by two different odd numbers (13 and 7), a first calculator A being provided to divide by the first factor, 13, and register the remainder or residue and a second calculator B deriving the residue (mod. 13Î7) and registering the number of thirteens in that residue. Calculator circuits.-The contacts PO to P9, Fig. 1, are closed by relays energized with the corresponding punch magnets and each provides a path from supply line 34 to check digit lines L1-L12. Relays 54 and 55 are energized when punch magnets for positions " O " and " X " are energized and both these relays are energized when the " Y " magnet is energized. Contacts of relays 54 and 54 modify the selection of the check digit lines. In addition, relay 56 has contacts which modify the selection so as to derive a complemented residue for subtracting the entered check digits. The lines L1- L12 then pass through further networks of relay contacts, the results of previous calculations being registered on the associated relays 40, 41, 42, 43, Fig. 2. The contacts merely derive from an entered number the residue (mod. 13) of the entered number Î 960 plus the number stored. A carry circuit to relay 44 is provided so that when the addition of two values in the calculator A exceeds 13 the B calculator total is advanced by one. The lines then pass through a network of diodes L1A, L1B to L12A, L12B, which recode the number to give the residue of ten times that number, which residue is stored in binary code in relays 35 to 38. The value in these relays is transferred to relays 40-43 between digits. The digits are also entered from contacts P0-P9 through one of three diode networks. The diode network to be operative is selected by relays 55, 56 mentioned above. When a check digit is being entered the diodes CD are operative, when relay 55 is energized, owing to the energization of an " X " or " Y " punch magnet for an alphabetical character, the O diodes are used. In other cases the third network (X) is used. The " O " and " X " networks convert the entered character to the residue (mod. 91) of the character times 960, and this registered in binary code on relays 45-47. The lower switching network in Fig. 3 sets up a group of relays 48-50 which modify the adding network of the B calculator in dependence on the results of the previous cycle's calculations in both A and B calculators. The upper network in Fig. 3 sets the B calculator relays 51-53 to the residue of ten times the entered value. Example.-A mixed item 6E is treated as a number of 60 plus the equivalent of E which, since it is represented by an " X " hole and a " 2 " hole, is 22. The item has an equivalent, therefore, of 82 and the check digit, 5 (residue, mod. 91, of 82 X 960), is associated with the item as 6E (05). When these digits are read-out in turn from store on to the punch magnets they also enter the A and B calculators as described. The A calculator produces from the first digit 6 a residue (mod. 13) of 1 which is stored on relays 40-53, Fig. 2, as ten. The B calculator, Fig. 1, responds by selecting a circuit through diode X6 to relay 46 representing 2. The upper network of Fig. 3 responds to the picking of relay 46 by entering 6 in the relay store 51-53. These figures of ten and six represent the residue (mod. 91) of 60. 60 x 960 divided by 9 leaves 88 which is expressed as 10 (in the A store) and 13 X 6 (in the B store). The character E is now entered, modifications by the " X " perforation causing both A and B calculators to respond as though a value of 22 had been entered. In the A calculator, contacts P2 select line L8 through normally-open contacts 54J. 8 is the residue (mod. 13) of 22 x 960. The adding circuit selects the line L5<SP>1</SP> and sets carry relay 44 to enter one into the B calculator. (10+8¸13=1 and a remainder of 5). The diode recoding network causes a value of eleven (residue mod. 13 of 5 Î 10) to be entered into the A store on relays 40-43. In the B calculator the closing of contacts P2 enters zero. Relays 52 and 53 are set up to store the value 6 from the first digit. Relays 41, 43 representing the value of ten in the A store are set up and the carry relay 44 is set up. The B calculator produces a value of three (relays 48, 49) so that the total amount registered is 11+3x13, i.e. fifty. This is ten times the check digit entered and since both calculators are modified during entry of check digits, as explained with reference to the numerical illustration above, so as effectively to subtract the check digit multiplied by ten, both calculators will register zero after the entry of the check digit. The correct entry of the number is thereby checked. Specifications 621,697 and 704,764 are referred to.