Leonardo da Vinci designed an odometer that released one pebble for each revolution of a measuring wheel.
The device was intended to measure distance traveled, especially along roads or during surveying. As the wheel turned, a geared mechanism transferred its motion to a container. After a set number of rotations, a pebble dropped into a box, providing a count that could be converted into distance.
Leonardo’s design shows how mechanical counting could turn wheel rotation into a practical measurement. It did not measure speed, because it recorded distance rather than distance divided by time. That distinction separates an odometer from a speedometer.
Ancient and later cultures also used wheel-based distance counters, so Leonardo should not be credited with inventing the general idea of measuring travel by wheel rotation. His drawings are notable for their detailed mechanical treatment of the counting mechanism.