892,424. Electric calculating apparatus. HAZELTINE CORPORATION. Aug. 6, 1958 [Aug. 22, 1957], No. 25184/58. Class 106 (1). A keyboard operated computor for performing the four rules of arithmetic and operating with binary numbers in the serial mode comprises, as shown in Fig. 4, a keyboard 11 on which four-digit decimal numbers are entered on keys 12A-12D (see also Fig. 1) and arithmetic operations are initiated by keys 13-18; a data-storage magnetic drum 30 with a section 31 on which the numbers 2<SP>m</SP> 10<SP>n</SP> (m, n=0, 1, 2, 3) for the decimarybinary conversion are permanently recorded in binary form as shown diagrammatically in Fig. 3b, a section 39 of four storage registers A-D for the binary numbers being operated upon, and a section 110 of clock and synchronization tracks; and the keys, switching relays, and gating and calculating circuits shown in Figs. 1 and 2. Addition and subtraction.- When a decimal digit key is depressed (such as key 7 in the units position as shown in Fig. 1) contacts of the series a-p are earthed according to its binary code, and these are contacted in turn by a contact 42 which together with a readhead 36 for drum 30 moves on an arm 145 along threaded rod 37 from right to left when control key 13 is depressed to energize relay 101 through rotor B of a stepping switch S1 and start a machine cycle. In synchronism with the contacting of a-p, read-head 36 reads the corresponding binary numbers on section 31 of drum 30 (each number occupying one half revolution on the helical track 33), and the circuit including contact 42, only the appropriate numbers are passed by amplifier 83 and gate 49 to adding circuit 50. The first-read number is passed unchanged by 50 and reversing circuit 53 and is recorded by head 44A on the A register, where it is read off ยข revolution (a minor cycle) later and fed through gate 59 and reversing circuit 56 to the second input of 50 and added to the number (if any) then being read from 31, the sum being entered in A; this process is repeated until the number entered on the keyboard has been accumulated in A. At the end of its traverse arm 145 contacts a plunger 136 which breaks switch S2a and deenergizes the traverse solenoid 101, closes S2b to energize K4 and step S1 to position 2 and closes S9 to energize reset mechanism 134 and carry 145 back to its initial right-hand position; also all keys are reset by mechanism 134 energized through wafer D of a switch S1. A second number can now be entered for addition to the first by depressing the appropriate digit keys and then the key 13 again, the total being accumulated in the A register by similar machine action. Subtraction is by addition of the 1's complement of the minuend which is effected by the energizing of relay K1 on depressing key 14 (after insertion of the subtrahend on the keyboard), this selecting the inverse outputs of reversing circuits 53 and 56, and passing the components of the subtrahend read from 31 successively to be added to the 1's complement of the partial differences in adding circuit 50, the 1's complements of the partial sums (i.e. the partial differences) being re-recorded in A, until the operation is completed. Printing.-Extraction of a number from register A for printing is by conditional subtraction; i.e. the numbers stored in section 31 are successively subtracted from the number registered (referred to as the minuend) and the result examined to see if it is positive, i.e. if the subtraction is proper. Depression of print key 19 energizes relay K2 which through contacts K2-1 enables amplifier 83 to pass all the numbers from 31, and K1 enabling subtraction (see above) of these numbers in turn from the minuend, the result being recorded in track A and the minuend (or partial difference) being re-recorded unchanged in track B through gate 77. If the result of the subtraction obtained on examination of its last (most significant) digit by passing a synch. pulse (occurring at the " last digit " time) and the subtraction result output to " and " gate 79 indicates a negative result, gate generator 64 is switched to close gate 59 and open gate 62 and hence pass the unchanged minuend for the next subtraction, also inhibit gate 81 is closed so that no output passes to 91. If the subtraction is proper, gate generator 64 receives a pulse through " and " gate 80 and the now open inhibit gate 81 to switch it to the state in which it opens gate 59 and closes 62 so that the new partial difference is passed to 50 for the next attempted subtraction, and output means 91 is energized. Output means 91 is shown in more detail in Fig. 1; it includes a two-wafer rotary switch 92 geared to make one revolution every two drum revolutions so that the rotor of wafer A contacts sectors 94-97 in synchronism with the contacting by 42 of the 8, 4, 2 and 1 contacts in each decimal denomination; at each proper subtraction relay K8 is energized and a voltage V from the right-hand print key contacts passes over an appropriate line to set (cumulatively in each decimal denomination) the printing mechanism 162, which is caused to print when rotor B contacts 98 and is reset when it contacts 99. The printer carriage moves one space at each revolution of the rotors. Multiplication is by successive addition of the multiplicand in A track to the partial product in D-track according to the digits of the multiplier in C track, the C and D track words being shifted one bit in the direction of increased significance every half revolution. The multiplicand is entered on the keyboard, and registered in storage track A by depressing key 15, and the multiplier similarly recorded in track C using key 16, after this switch S2b closes to step S1 to position 2, but when the arm 145 returns to its rest position S3 closes and steps S1 on to position 3 and re-energizes solenoid 101 for a further translation of head 36. In this translation the multiplicand and multiplier are re-circulated until arm 145 closes switches S4 and S7, when relay coil K6A of latching relay K6 is energized switching the K6 contacts to the positions other than those illustrated. This brings into action recording elements 46C and 46D which are offset by one bit to effect shift in the direction of increasing significance of the contents of the C and D tracks each half revolution of the drum. A synch. pulse coinciding with the first binary digit from A track is applied to " and " gate 73 which also receives the successively shifted multiplier read from the C track and passed unchanged through adding circuit 74, and hence activates gate generator 72 to enable " and " gate 70 for one word period so that the multiplicand from the A track is passed through gate 82 to adding circuit 104 for accumulation in D track. At the end of the multiplication arm 145 operates switch S5 to energize latching relay coil K6B so that recording is again by heads 44C and 46C, and opens S2a to return 145 to its initial position, and S2b energizes K4 to switch S1 to position 5, and on return of arm 145, S7 closes to step it to position 6 when K5 connects adding circuit 50 to D track amplifier 87 so that the product is transferred to the A track, and finally S3 closes to step S1 to position 7 for resetting the keyboard through rotor D. The product is now ready for printing. Division is by successive attempted subtraction of the shifted divisor from the dividend, using conditional subtraction as in the printing routine. The dividend is entered with its first significant decimal digit on unit 12D, and the divisor with its first on 12C (three significant decimal figures only) so that it requires only eleven bits (half the computor capacity); they are recorded in the A and C tracks as in the multiplication routine above, after which K6A is energized through S6, and for the first eleven half revolutions of the drum the divisor is advanced to be aligned with the dividend, when 145 closes S7 to energize K4 and advance S1 to position 4 and energize K9 over rotor C to route the stored information for conditional subtraction (K1 has also been energized by key 18 to effect subtraction by adding circuit 50 from the dividend or partial remainder in A track of the divisor in C track), and switch to record head 47D for shifting of the stored quotient digits. The quotient is built up in D track from output pulses from gate 81 indicating proper subtraction (see print routine above) via adding circuit 104. Division is completed when arm 145 depresses plunger 135 to step S1 to position 5, de-energizing K9 and energizing K5 so that the quotient is recorded in the A track for printing.