Uploaded January 2022 | Updated September 2026, 1 hour ago

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The Sumlock was made by Bell Punch in the UK from 1940 till the late 60s. It is used exactly like the Comptometer. Here is the first model (1940-1945, made by subsidiary London Computator Corporation) and the last model (1953-1970).

Errata: There are of course 20 shillings in a pound, not 19.

For more information about this machine and others in my collection, please visit my website:
jaapsch.net/mechcalc

0:00 Introduction
0:22 British currency
1:22 Error detection
2:47 Model 913!?
4:22 Model F or SF
4:55 Error on new model
6:00 Outro