Leibniz wheel

A Leibniz wheel or stepped drum is a cylinder with a set of teeth of incremental lengths which, when coupled to a counting wheel, can be used in the calculating engine of a class of mechanical calculators.

Invented by Leibniz in 1673, it was used for three centuries until the advent of the electronic calculator in the mid-1970s.

[1] It was made famous by Thomas de Colmar when he used it, a century and a half later, in his Arithmometer, the first mass-produced calculating machine.

The computing engine of an Arithmometer has a set of linked Leibniz wheels coupled to a crank handle.

From the late nineteenth century on, Leibniz stepped drums in purely mechanical calculators were partially supplanted by pinwheels which are similar in function but with a more compact design; stepped drums remained the primary technology for electromechanical calculators until the development of purely electronic calculators.

In the position shown, the counting wheel meshes with three of the nine teeth of the Leibniz wheel.
Replica of Leibniz's Stepped Reckoner in the Deutsches Museum .
Thomas de Colmar Arithmometer (from 1852, significantly different from his 1820 model) uses Leibnitz stepped drum. Considered by many to be the first largely successful mechanical calculator, and the first to be produced in large numbers (thousands)