GB1293376A - Improvements in or relating to calculating machines - Google Patents

Abstract

1293376 Rounding off BELL PUNCH CO Ltd 3 July 1970 [3 July 1969] 33659/69 Heading G4A A digital electric calculator includes a means for rounding off numbers stored in a register by adding 5 into the decimal place below the last such place to be retained in the rounded off number, adding in any resulting carry, and clearing all the non-required stages to zero. Provision is made for shifting the answer, which may be displayed on a set of digit indicating tubes, one place to the right if any carry ripples through to the most significant digit of the number. The number of places to which rounding is to be made can be varied by connecting the corresponding number of gates to a counter so that depression of a rounding key feeds the corresponding number of pulses to a counter. Two further counters providing sequential outputs on a number of leads equal to the number of stages in the register holding the number to be rounded are provided, the number of pulses stored in the first counter causing the outputs of the further counters to be relatively displaced. The outputs of these two counters, together with shift pulses gated to the register each time the counter outputs change control the rounding. The register contents are circulated until the counter outputs indicate that the most significant digit to be cleared is in a register stage connected to an adder. A factor of five is then added to that stage and any carry resulting from the addition is propagated until the most significant digit of the number has been processed. When the register is circulated one more place the counter outputs initiate clearing of the portion of the number not required by causing a circuit to pulse all the non-required digits to zero. During the carry propagation an extra shift one place to the right is initiated if an additional place is created by carry ripple through.