Plus & Sumlock Mechanical Calculators
Plus 512/S Sterling currency calculator

Plus 512

PLUS model 512/S Sterling currency "Comptometer".

Sterling currency, key-driven ("Comptometer") type, with abbreviated keyboard (only has keys 1 to 5) extended to 9 decades of £'s.  To enter a number greater than 5 two or three keys have to be pressed in succession in that column.

185 mm x 180 mm x 127 mm (7.5" x 7" x 5").

Made by Bell Punch Co. Ltd, distributed by Sumlock Comptometer Ltd.

The machine illustrated has serial number 512/S/876.135, and has the angular style casing which was introduced in 1958.

To enter a number above 5 the operator has to press two keys in that column which add up to the number required.

To enter 11 in the Pence column the operator has to press 3 keys !!, eg. (5)+(5)+(1).

This has little effect on the speed of addtion operations but severly affects the processes of subtraction, multiplication, and division.

The machine in the photograph above shows the total £125/17s/11d


See the Old Sterling Currency section for more information on the pre-decimalisation money system used in Britain and the British Commonwealth.

Note the use of plastic gears (cheaper) in the photograph of the mechanism, below.

With cover removed
The labels underneath

The labels underneath, showing Manufactured by the Bell Punch Company Ltd., and Distributed by Sumlock Comptometer Ltd.

Note 1 - Both of these companies were owned by the holding company Control Systems, Limited.

Note 2 - The use of Comptometer in the name of Sumlock Comptometer - This had been a trade name of the Felt & Tarrant Manufacturing Company who had originated the Comptometer. See the All Change at Bell Punch section of this site.

There are excellent photographs and descriptions of the Plus Adder mechanism at John Wolff's Web Museum site. These are accessed from the Comptometers and Key-Driven Calculators section on that site.

Click here to go to the Vintage Calculators Web Museum

Text & photographs copyright © 2002 - 2023 Nigel Tout, except where noted otherwise.