Geared carries
Wheels marked with the digits 0 to 9 automatically turned the next wheel by one step when they went from 9 to 0. Today's processors use the same “carry” principle, only electronically.
Leibniz and binary
Gottfried Wilhelm Leibniz improved the machine so it could multiply, and he also described the binary system of zeros and ones. 250 years later it became the language of every computer.
A calculator for your pocket
The Curta calculator of 1948 was a small cylinder operated by turning a crank. Rally drivers found it indispensable until electronic calculators with chips pushed it out in the 1970s.