Gottfried Wilhelm Leibniz (Leipzig, 1646 – Hannover, 1716) designs the Stepped Reckoner (Staffelwalze) and presents a prototype to the Royal Society of London in 1673. Its central mechanism is the Leibniz wheel: a cylinder with teeth of increasing length that allows mechanical multiplication and division, not just addition and subtraction. It is the first calculator capable of performing all four arithmetic operations through a single mechanism. The Leibniz wheel becomes a standard component of mechanical calculators for two centuries: it is present in Thomas de Colmar's arithmometer (1820), in Brunsviga machines, and in the Millionär (1893). A surviving Stepped Reckoner is preserved at the Leibniz-Bibliothek in Hannover.