Operating a Comptometer

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

Plus 512

PLUS model 512/S/876.135 Sterling currency "Comptometer".

This is an Abreviated-Keyboard Sterling type "Comptometer", with 9 decades of £'s.

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

This style of casing was introduced in 1958.
Made by Bell Punch Co. Ltd, distributed by Sumlock Comptometer Ltd.

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.

Origins of Bell Punch Co.
All Change at Bell Punch
Development of Anita 1
Development of Anita 2
Anita is Launched
At work with Anita
National Calculating Service
Anita Developed Further
Anita at its Zenith
The Rockwell Connection
Demise of Anita & Bell Punch
Mechanical Calculators
Early Anita Desktop Calculators
Transitors & Integrated Circuits
Anita LSI Desk Calculators
Anita Hand-held Calculators
Rockwell-Anita Calculators
Calculators made by others
The Technology Explained
Operating a Comptometer
Old Sterling Currency, £sd
Update Information

Plus & Sumlock Mechanical Calculators

Petter S
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Plus 509
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Plus 512
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Sumlock 912 Weight Calculator
Sumlock Comptometer 993m
Sumlock Comptometer 993s

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Text & photographs copyright © 2002, 2003 Nigel Tout, except where noted otherwise.