To follow-up on the mechanical calculator presented here a few weeks ago, let’s have a quick look at a circular slide rule. Sure we all know the classic slide rule – such as the Hemmi bamboo one owned by my dad.

The КЛ-1 demonstrated here is a common Russian model, built like a pocket watch and is capable of multiplications, divisions (as well as combinations of those – see the video), squaring/square root finding and basic trigonometry. This specific model is commemorating the 50th anniversary of the October 1917’s revolution.