Jaap Scherphuis | The Sumlock mechanical calculator, and some advanced calculation techniques. @jaapsch2 | Uploaded January 2022 | Updated October 2024, 4 minutes ago.
The Sumlock was made by Bell Punch in the UK from 1940 till the late 60s, but these two were made in the early 1950s. They are used exactly like the Comptometer. After a short demo, I show how to multiply the register result by another number, and explain division in a bit more detail.

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

0:00 Introduction
0:26 History
0:59 Overshoot prevention
1:40 Error detection
2:31 Models
2:58 Multiplication
4:59 Division
9:50 Outro