Leonardo da Vinci’s odometer was a wheel-based device designed to estimate distance by counting wheel rotations.
Leonardo’s design combined a cart wheel with a gear mechanism. As the wheel turned, the gears advanced a container or indicator by a fixed amount. The device could therefore translate repeated wheel rotations into a distance estimate, much like the basic principle of an odometer in a modern vehicle.
The instrument was especially useful for mapping and surveying, fields in which Leonardo produced detailed studies. Its accuracy would have depended on the wheel’s circumference, the gear ratio, and the ground surface. Slippage or uneven terrain could make the result less precise.
Leonardo did not invent the general idea of measuring travel with a wheel; earlier devices existed. His importance lies in the clarity and mechanical sophistication of his surviving design, which shows how gears could automate measurement.