Patent GB-665046-A (GB)
Title: Improvements in and relating to electrical calculating machines
IPC: G06F7/46
Filed: 1949-09-12
Abstract: 665,046. Calculating apparatus. BRITISH TABULATING MACHINE CO., Ltd. Sept. 12, 1949 [Sept. 22, 1948], No. 23489/49. Class 106 (i). Apparatus for multiplying or dividing two factors comprises a multiplier accumulator settable to represent a multiplier, a product accumulator for representing the product, both adapted to receive positive or negative entries for algebraic summation, means for reducing the amount in the multiplier accumulator to an amount representing zero by successively entering therein amounts automatically selected representing plus or minus 1, 2, 5 or 10 or their multiples by 10 and its powers, and means for entering into the product accumulator multiples of the selected amounts by the multiplicand. Apparatus for dividing one factor by another comprises similar accumulators for representing the dividend and quotient, respectively, means for entering into the quotient accumulator amounts automatically selected representing plus or minus 1, 2, 5, .2, .5 or their multiples by 10 and its powers, and means for entering into the dividend accumulator multiples of the said amounts by the divisor, the entries being con. tinued until the dividend accumulator contains a positive true amount less than the divisor. Means may be provided, controlled by the value of the highest significant digit in the multiplier accumulator and the sign of the amount therein for selecting which of the amounts plus or minus 1, 2, 5 or 10 shall be entered into the multiplier accumulator when multiplied by the appropriate power of 10, and column shift means controlled by the denominational order of the highest significant digit in the multiplier accumulator, for multiplying the selected amount by the appropriate power of 10, and similarly in the case of a dividing operation. Figs. 2 and 4 set forth the mathematical procedure involved in carrying out a specific example of multiplication and division, respectively. The accumulator mechanism is of the type described in Specification 483,021, one unit of which is shown in Fig. 7, each wheel 14 being connected to so-called read-out brushes 26, shown diagrammatically in Figs. 1c and 1e. The separate units or orders are grouped to form several accumulators designated as ACC1, ACC2, ACC3 and ACC4 (Figs. 1c and 1e). Referring to Fig. 2, the factors 789 and 87693 are to be multiplied. The multiplier is set in a multiplier accumulator. Amounts representing plus or minus 1, 2 and 5 or their multiples by 10 and its powers are successively subtracted from the value in the multiplier accumulator until the value therein is reduced to zero, and multiples of these amounts by the multiplicand are added into the product accumulator. The process may be set out thus : (100,000 - 20,000 + 5000 + 2000 + 500 + 100 + 100 - 10 + 5 - 2) 789 or (80,000 + 7000 + 600 + 90 + 3) 789 = 87,693 x 789. In the example given the highest digit of the multiplier is plus 8, accordingly the amount 10 is selected and multiplied 10,000 to bring the 0 of the 10 into the denomination of the 8, the amount 100,000 is then subtracted from the multiplier, leaving a negative remainder of 12,307. Concurrently with this subtraction 100,000 times the multiplicand 789 is entered into the product accumulator in appropriate denominational allocation so that after the first step or cycle of operation the multiplier accumulator contains the negative remainder and the product accumulator contains what is in effect 100,000 times the value of the multiplicand. A further inspection of the highest digit of the remainder shows it to be a negative 1 which selects an amount of -20,000, accordingly - 20,000 is subtracted leaving a positive remainder 7693. Concurrently - 20,000 times the multiplicand is entered in the product accumulator with the positive result of 63,120,000. At this point the product accumulator represents 100,000 times minus 20,000 times or 80,000 times the multiplicand. The third selection in accordance with the plus digit value 7 selects a multiplier of 5000 which is subtracted in the multiplier accumulator to obtain the positive remainder 2693 and the concurrent entry of 5000 times the multiplicand advances the product accumulator to 67,065,000. Continuing, the repeated inspection of the successive remainders and entry of the 1, 2 and 5 multiplies of the multiplicand, together with entry of the 1, 2 and 5 digits will cause the multiplier ultimately to reduce to 0 and for the example given the product accumulator will stand at 69,189,777 at such time to represent the final product. It is more convenient to enter the factors into the accumulators in the form of their complements to 9 providing as is usual for a carry from the highest denomination to the lowest. The accumulator settings in complementary form are shown in Fig. 3 which is equivalent to the operations shown in Fig. 2 if it be noted that a positive member in true form may be regarded as a negative number when it is in complementary form and vice versa.