What counting machine did Leonardo da Vinci sketch using numbered rods and gears?

Leonardo da Vinci sketched a mechanical calculator using numbered rods and gears.

A drawing in the Codex Madrid describes a machine with geared mechanisms intended to perform arithmetic operations. The design is commonly discussed as an early calculating-machine concept because rotating components could represent numerical values and transfer quantities from one place to another.

Leonardo’s sketch is not a complete operating manual, and historians debate how much of the surviving drawing represents a finished design. It does not prove that he built a working calculator. The machine is nevertheless important because it shows his interest in automating repetitive mathematical work through mechanical motion.

This invention should not be confused with the abacus, which uses manually moved counters, or with Blaise Pascal’s Pascaline, built in the seventeenth century. Leonardo’s calculating device predates Pascal’s machine by more than a century, but no surviving Leonardo calculator is known.