What machine did Leonardo da Vinci sketch for adding and subtracting numbers mechanically?

Leonardo da Vinci sketched a mechanical calculator for carrying out arithmetic with rotating wheels and gears.

The design appears in Leonardo’s notes from around 1500 and is commonly associated with a device that could add numbers through linked gear mechanisms. It is sometimes called Leonardo’s calculator or Leonardo’s calculating machine. The surviving drawings are not a complete operating manual, so historians are cautious about claiming exactly what the finished machine could do.

The idea belongs to the early history of mechanical computation. A mechanical calculator represents numbers physically, often through the positions of wheels, and uses controlled movement to produce an arithmetic result. This differs from an abacus, where a user moves beads, and from a slide rule, which uses logarithmic scales rather than toothed gears.

Leonardo’s sketch predates the well-documented seventeenth-century calculators of Wilhelm Schickard and Blaise Pascal. It should therefore be described as an early calculator concept, not as proof that Leonardo built the first fully working calculator.