Curta

 The Curta is a small mechanical calculator developed by Curt Herzstark. The Curta's design is a descendant of Gottfried Leibniz's Stepped Reckoner and Charles Thomas's Arithmometer, accumulating values on cogs, which are added or complemented by a stepped drum mechanism. It has an extremely compact design: a small cylinder that fits in the palm of the hand.

Curtas were considered the best portable calculators available until they were displaced by electronic calculators in the 1970s.

Design

Numbers are entered using slides (one slide per digit) on the side of the device. The revolution counter and result counter reside around the shiftable carriage, at the top of the machine. A single turn of the crank adds the input number to the result counter, at any carriage position, and increments the corresponding digit of the revolution counter. Pulling the crank upwards slightly before turning performs a subtraction instead of an addition. Multiplication, division, and other functions require a series of crank and carriage-shifting operations.

The Curta was affectionately known as the "pepper grinder" or "peppermill" due to its shape and means of operation. It was also termed the "math grenade" due to its superficial resemblance to a certain type of hand grenade.

                                                                                                                source:wikipedia.org