What mechanical calculator did Leonardo da Vinci sketch with numbered wheels for performing arithmetic?

Leonardo da Vinci sketched a calculating machine with numbered wheels intended to represent and manipulate numbers.

The drawing appears in the Codex Madrid, a collection of Leonardo's notebooks rediscovered in the twentieth century. Its geared wheels suggest a device for carrying out arithmetic mechanically, although the exact intended operation and whether Leonardo completed a working prototype remain uncertain.

The design is significant because it shows Leonardo applying gears, positional representation, and controlled rotation to calculation. Those ideas later became important in mechanical calculators. Historians must distinguish the surviving sketch from a documented working calculator: the evidence supports a design concept, not confirmed widespread use.

It is also different from an abacus, which uses manually moved counters, and from the Pascaline, a later working calculator associated with Blaise Pascal. Leonardo's machine belongs to the early history of mechanical computation.