This half page trader advert from
June 1951 shows the predecessor of the pocket calculator. I think
I've seen one of these once. You use the "pen" to drag
down the roll-over numbers; this causes the next column to increment when
Rapid Adding & Subtraction Machines
For book-keeping and
stocktaking in shops, offices and factories.
Can be mastered in a few
operation. No keys to punch.
immediately. Totals always visible.
Cannot make a mistake.
£6 - 6 - 0
Immediate delivery at a price
even small businesses can afford from
K. Bisset & Co., Ltd., (Dept. W.) 5, Chelwood Gardens, Kew Gardens,