Plus & Sumlock Mechanical Calculators
Sumlock 912/Y Imperial-Weight Calculator

Sumlock 912 Imperial-Weight Calculator

SUMLOCK model 912/Y 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.

The machine illustrated has serial number 912/Y/122703.

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.


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.

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