Patent GB-1071726-A (GB)
Title: Improvements in or relating to calculating apparatus
IPC: G06F7/48
Filed: 1965-09-15
Abstract: 1,071,726. Digital electric calculator. WANG LABORATORIES Inc. Sept. 15, 1965 [Sept. 22, 1964], No. 39357/65. Heading G4A. A digital electric calculator for obtaining logarithm to a base B from a number to a base R comprises a first register containing the number to the base R, a second register receiving the logarithm, a memory containing specified constants in the base R and the logarithms to the base B of the said constants and means for multiplying the number in the first register by said constants to obtain a result as near to 1À000 as desired at the same time adding or subtracting the appropriate logarithmic value to or from the second register. As described constants in the form of 1Œ<SP>1</SP>/R<SP>A</SP> are used, i.e. 0À9, 1À01, 0À999, 1À0001. As described, a number to the base R is entered in register 14 and shifted left or right until the most significant digit is between 0À1 and 1À0 (i.e. multiplying or dividing successively by R) and for each multiplication or division the logarithm of R to the selected base B is subtracted or added to register 16 which previously held zero. The number is then successively multiplied by 2 and log 2 is subtracted from register 16 for each step, the operation ceasing when the number in register 14 is greater than or equal to 1. The number is then successively multiplied by 0À9 until it becomes less than 1 and log 0À9 is added to Register 16 for each step. The multiplications proceed with 1À01, 0À999 &c. until the number in Register 14 is as near 1À0000 as desired. The number in Register 16 is then the corresponding logarithm to the base B. A similar procedure may be used for antilogarithms. The original number entered in register 14 may have its decimal point identified by a number in decimal point storage register 84. The number may then be shifted until register 84 becomes zero to produce an output on line 110 which sets flip-flop 102 to alter a step programmer 90 to cause the next stage to be applied. Further alterations of the step programmer may be caused when the most significant digit M of register 14 changes from 0 to 1 or vice versa. Multiplication by 2 is obtained by adding the contents of the register to itself and by 0À9 by subtracting <SP>1</SP>/ 10  of the contents from the contents of register 14. The tenth is obtained by shift of one order by delay 96 and inserting the delayed quantity through adder 72 in a subtraction operation. During addition or subtraction data on line 76 may be serially added to the contents of the shift registers as transferred from the least significant stage L via the adder and replaced in the most significant stage. Alternatively a parallel adder may be used. Data may be entered from a manually operated keyboard which also has cathode-ray tube or Rixie tube display devices or may be entered from tape. Decimal numbers are entered in the binary decimal system. Squaring or square rooting may be done by doubling or halving the log of the number. The logarithm of a logarithm may be calculated. A time shared adder may be used instead of adders for each of the registers shown. Programming may be determined by tape input or a manually operated desk control.