1) Mechanical calculator 
The Curta is a small, hand-cranked digital mechanical calculator introduced by Curt Herzstark in 1948. 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, accu......