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.