GB1184498A - Calculating Apparatus. - Google Patents

Abstract

1,184,498. Determining check digits. NATIONAL RESEARCH DEVELOPMENT CORP. .18 Oct., 1968 [3 Oct., 1967], No. 45043/67. Heading G4H. Apparatus for determining the check digit of a number comprises a plurality of groups of selection means, e.g. selector switches, one group for each of the digits of the number, the selector 100 corresponding to the highest significant digit giving a remainder signal which selects one of the next group of switches, these corresponding to the next digit, the selected switch giving a remainder signal selecting one of the next group and so on, the ouput of the selected switch 400-410 of the last group giving an output to indicate the check digit. The check digit is calculated by multiplying each digit by a factor, the units digit by 2, the tens by 3, the hundreds by 4 the thousands by 5 and so on. The sum of all the products is divided by 11 and the remainder is subtracted from 11 to obtain the check digit. The sum of all the products and the check digit will then divide exactly by eleven. The apparatus is arranged to give a remainder for each digit in turn, passing it on to the next. The thousands digit is set up on dial 111 and switch 100 then gives the remainder when the digit is multiplied by 5 and the product divided by 11. The hundreds digit is set up on dial 222, the remainder when the digit is multiplied by 4 and the product divided by 11 appearing on switch 200. However, the remainder from the previous digit must be added and the present remainder adjusted accordingly. The switch 20 (ganged to switch 200) corresponds to a previous remainder of 1; switch 202, of 2; switch 203, of 3, and so on. The appropriate switch 200-209 is selected by the selected output lead of switch 100 and the selected switch then selects an output lead which, in turn selects a switch in the next group 300-310. This group corresponds to the tens digit and gives the remainder of the previous remainder plus the tens digit multiplied by 3, all divided by 11. The remainder signal selects one of the switches in the units group 400-410 which produces a remainder output in a similar way. This output is the 11's complement of the required check digit and the selector switches may be connected to suitable indicators showing the check digit, e.g. a remainder signal on a "2" lead would light a "9" indicator. To check a check digit it is set up on dial 555. One of the selector switches (selected by the output from the selected one of units switches 400-410) then connects to lamp 14 which lights when switch 15 is closed. If the check digit is incorrect, lamp 16 lights. Instead of selector switches diode or transistor logic circuits may be used.