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Sumlock Abbreviated-keyboard Sterling "Comptometer"

Abbreviated Sumlock Comptometer

Lower-cost, Abreviated-Keyboard, key-driven adders of the "Comptometer" type were produced with only 5 keys per column.

Illustrated is an Abreviated-Keyboard Sterling type calculator (model PLUS 512/S/876.135, made by Bell Punch Co. Ltd, distributed by Sumlock Comptometer Ltd., both owned by Control Systems Ltd.).

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

Manufactured in the 1960's.


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

To enter 11 in the Pence column the operator has to press 3 keys in succession!!, eg. (4)+(4)+(3).

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

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


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.

For information about the Bell Punch company and its calculators see the article on this site "Anita: the world's first electronic desktop calculator - A brief history of the complex Bell Punch company and its calculators".

For a detailed history of the development of the Bell Punch and Anita calculators go to the associated site "Bell Punch Company and the Anita Calculators".

There are instructions for the basic use of Comptometer-type machines in the article "Operating a Comptometer" on this site.

Click here for more information about Comptometers.

Vintage Calculators

Text & photographs copyright, except where stated otherwise, © Nigel Tout 2000-2024.