Operating a Comptometer

Plus & Sumlock Mechanical Calculators
Sumlock 912 Imperial-Weight Calculator

Sumlock 912 Imperial-Weight Calculator

SUMLOCK model 912/Y/122703 Imperial-Weight "Comptometer"

This is a direct action keyboard calculator of the "comptometer" type with a keyboard for calculations in Imperial weight units.

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.

Imperial weight units work like this:
One Ton = 20 Hundred-weights (cwt.) [= 2240 Pounds (lbs.)]
One Hundred-weight (cwt.) = 4 Quarters (qtr.) [= 112 Pounds (lbs.)]
One Quarter (qtr.) = 28 Pounds (lbs.)
One Stone = 14 Pounds (lbs).

The keyboard of this machine (see below) has keys with, from the left, 7 columns of Tons keys, 2 columns for Hundred-weight keys, 1 column of Quarters keys, and 2 columns for the Pounds keys.
Yes, the single key in the second column from the right has "14" on it, which is the number of Pounds in one Stone. The value in this column has to be mentally added to the number in the right-most column. There is carry over when this sum reaches 28 into the third column from the right (ie. Quarters).

The machine in the photograph displays the total of 10 Tons, 19 Hundred-weights, 3 Quarters, and 23 Pounds.


The strange keyboard of this Imperial weight calculation machine.

Origins of Bell Punch Co.
All Change at Bell Punch
Development of Anita 1
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Anita is Launched
At work with Anita
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Anita Developed Further
Anita at its Zenith
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Mechanical Calculators
Early Anita Desktop Calculators
Transitors & Integrated Circuits
Anita LSI Desk Calculators
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Rockwell-Anita Calculators
Calculators made by others
The Technology Explained
Operating a Comptometer
Old Sterling Currency, £sd
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Text & photographs copyright © 2002, 2003 Nigel Tout, except where noted otherwise.