What calculating device did Leonardo da Vinci sketch using a series of geared wheels?

Leonardo da Vinci sketched a mechanical calculator using geared wheels to represent and perform numerical operations.

The drawing, recorded in the Codex Madrid, shows a system of gears and numbered elements that could potentially carry values from one place to the next. Its arrangement is commonly interpreted as a calculating machine, although Leonardo did not leave a complete operating explanation.

Because the surviving sketch is incomplete, historians should distinguish between a calculator design and a proven working calculator. It is not evidence that Leonardo built a functioning desktop machine or that he invented every principle used in later mechanical arithmetic.

The concept belongs to a long history of calculation tools that includes the abacus, Napier’s bones, and Blaise Pascal’s Pascaline. Leonardo’s proposal is notable because it applies precise gear motion to numerical computation centuries before electronic calculators.