Patent GB-724137-A (GB)
Title: Improvements in or relating to decimal point location in electronic computers or other data-handling devices
IPC: G06F3/027
Filed: 1952-06-24
Abstract: 724,137. Digital electric calculating-apparatus. MONROE CALCULATING MACHINE CO. June 24, 1952 [Feb. 9, 1952], No. 15865/52. Class 106 (1). A decimal-point aligning means for use in an electronic computer or other data-handling device having a storage device in which digit signals representing a number are registered, comprises a counter which is advanced one step for each digit on one side of the decimal point of the number and is further advanced up to a predetermined count, the registered digits being processed one digit space for each step of the further advance. The apparatus shown in Fig. 1 includes a singlebank decimal keyboard 25 and control circuits including 27 and 47 which consist primarily of bi-stable trigger pairs (TP) of triodes (or bistable relay devices), " or " gates (V), coincidence gates (G) and polarity-inverting circuits (I). Digits are entered one by one from the keyboard 25 in binary-coded form into a temporary store 26, starting from the highest or lowest denomination. The decimal point is entered by key 45 and, after the whole number has been entered, a key 44 is operated which causes the number in the store 26 to be precessed so as correctly to position the decimal point, and then to be transferred to a track of magnetic drum 28 selected by relay circuit 30, under control of cycle counter 43. The store 26 may be a shift register but, as particularly described, comprises a rotating magnetic disc on which magnetized spots of opposite polarity to represent " 1 " and " 0 " are recorded, one during each of the 180 time periods t0-t179of the disc cycle, under control of pulses R, Fig. 2, from pulse generator 29a whose input is obtained from a track a on the drum 28. Recording and playback means are so spaced around the magnetic disc that a recorded spot is re-recorded during an " active cycle " 92 time periods later, and again 4 time periods later during the next active cycle, which corresponds to a precession of one decimal digit space. Each decimal digit is translated by a diode matrix arrangement (Fig. 3, not shown) in the keyboard into combinations of signals on four lines corresponding to 1, 2, 4, 8 which are gated during periods t0-t3 respectively, a " 0 " being recorded in the absence of a " 1 " signal from the keyboard. Up to a twenty-digit number may be stored (ten digits on either side of the decimal point), the number being transferred to the drum 28 during periods t4- t83 of a cycle. The cycle periods are marked by a counter 34 which receives pulses C, Fig. 2, from circuit 29a and controls a matrix 37, e.g. a diode network, to produce gate-controlling outputs as indicated. Whenever the counter 34 reaches 179, gate 33 and, through inverter 40, gate 38 are closed to stop the supply of pulses C and R and thus further operation of the counter and the store 26, but if the next cycle is to be active, a pulse over line 36 from Go circuit 27 causes the counter to jump from 178 to 255 (its capacity) instead of 179; this pulse Z ,Fig. 2, is produced in response to a pulse C applied to a coincidence gate controlled by a trigger pair TP (not shown) operated during each time period t178 by a pulse ZD from a track b of the drum 28 through generator 29b, and reset by the next pulse A at the beginning of t178 (or t255), and is allowed to pass to the line 36 and also to step on cycle counter 43 if a digit key or key 44 has been depressed. Timing pulses G, Fig. 2, also are supplied from circuit 29a to Go circuit 27. As an example of operation, suppose the number 62.7421 is to be entered beginning with the highest denomination. After the " 6 " and " 2 " have been entered, " 3 " is registered on the cycle counter 43 and " 62 is recorded in the store 26 in positions corresponding to t0- t7. Depression of the decimal point key 45 operates reset circuit 47 to reset counter 43 to its initial value " 1," and after entry of the four decimal digits 7, 4, 2, 1 the counter registers " 5 " and the number is stored in positions t0-t23. Depression of key 44 initiates a succession of active cycles counted by counter 43, during each of which the number is precessed four time periods, which continue until the counter reaches " 12 " whereupon it is automatically reset to " 1 " and gate 31 is opened to transfer the number in the store to the drum 28, the number being then shifted so as to appear in time periods t28 -t51 with the decimal point in its correct mid-position between t43 and t44À For entry of a series of numbers having the same number of digits before the decimal point a switch 46 can be pre-set so as automatically to reset the counter 43 after a predetermined number of digits (counted by 43) have been entered. This enables significant zeros, e.g. in the number 75,000, to be entered automatically. A modification without the switch 46 is described (Fig. 8, not shown) in which digits on one side only of the decimal point are counted. Various interlocking connections are provided in the control circuits 27, 47 associated with the keys 44, 45 and switch 46, and with a " compute switch " (not shown) operated after the completion of keyboard operations. Reference is made to the use of a tape reader instead of a keyboard. Specification 692,912 is referred to,