Plus & Sumlock Mechanical Calculators
Sumlock 912/S Sterling Currency Calculator

Sumlock 912

SUMLOCK model 912/S British Sterling currency (£sd) "Comptometer".

This is a full-keyboard direct action keyboard calculator of the "comptometer" type  for Sterling currency calculations.

It is a model 912/S where the 9 denotes the full keyboard (keys up to 9), the 12 denotes the 12 columns of keys, and the S denotes a Sterling currency version.

330 mm x 315 mm x 135 mm (13" x 12.5" x 5.5"), 7 Kg (15.5 lbs).

Manufactured about the 1950's-1960's.
Made by Bell Punch Co. Ltd. in Britain, distributed by Sumlock Ltd.

The machine illustrated has serial number 912/S/4AH/120.260.

This machine has a full keyboard except for the Pence column where there are only 9 keys (1-9) instead of 11 in a fully keyed model, although the accumulator for this column will display up to 11. The tens of shillings column only has the one key necessary.

To enter 11 in this column the operator has to press in turn the (9) key and the (2) key.

This plays off ease of use compared with lower manufacturing cost in that more standard components can be used.

The machine in the photograph displays the total of £1,500/17s/11d.

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


The Sterling currency keyboard (£sd), with the rightmost column limited to the keys 1 to 9, instead of the 1 to 11 in a fully keyed model.

The small numbers, to the left on each key, are used for subtraction.

Cover removed

Here the base has been removed. All of the mechanism is attached to the top plate with the keys.

The mechanism

The mechanism from below. Each column has an identical assembly of gears and levers.

There is an operating manual for the Sumlock "Comptometer"-type machine in the Operating Manuals section of this site, with a summary on the Operating a Comptometer page.

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