The Curta is a small, hand-cranked mechanical calculator introduced in 1948. It has an extremely compact design – a small cylinder that fits in the palm of the hand.
It can be used to perform addition, subtraction, multiplication, division, and, with more difficulty, square roots and other operations. The Curta’s design is a descendant of Gottfried Leibniz’s Stepped Reckoner and Thomas’s Arithmometer, accumulating values on cogs, which are added or complemented by a stepped drum mechanism.
Read more about Curta calculator on Wikipedia.