What mechanical instrument did Leonardo da Vinci design to add numbers automatically?

Leonardo da Vinci designed an early mechanical calculator for adding numbers automatically.

His 1490s notes include a device built from linked wheels and gears. Turning one wheel would transmit movement to another, creating a mechanism capable of representing numerical operations. The design is often described as an early adding machine or mechanical calculator.

Leonardo did not leave a complete operating calculator with a surviving instruction manual, so historians reconstruct the device from his drawings and notes. A working model made in the 1960s demonstrated that the mechanism could function in principle.

This invention should not be confused with the abacus, which requires a user to move beads, or with later calculating machines that performed multiplication and division more directly. Leonardo’s design belongs to the long history of geared calculation machines that eventually led to electronic calculators.