Uploaded January 2026 | Updated September 2026, 1 hour ago

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The Addo Primary Calculator is a simple toy adder. It was made in 1964 by the British branch of the Swedish Addo company which manufactured office adding machines.

The mechanism is very similar to Hart's Mercantile Computing Machine. See @stephenfreeborn Stephen Freeborn's video: youtube.com/watch?v=-3JQoArQo3A

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

0:00 Introduction
0:51 Addition
1:51 Multiplication
2:33 Subtraction
3:35 Mechanism
5:33 Manual and article
6:31 Outro