Leonardo da Vinci designed an odometer that measured distance with a wheel and falling stones.
In his design, a wheel turned as a vehicle moved. Gears transferred the wheel’s rotation to a mechanism that released a stone at regular intervals into a container. Counting the stones therefore indicated how far the vehicle had traveled. The device was intended for surveying and road measurement rather than for modern automobile dashboards.
An odometer measures distance traveled, while a speedometer measures speed and a compass indicates direction. Leonardo’s design shows how counting repeated mechanical movements can turn motion into a numerical result. The basic idea—using wheel rotation to estimate distance—remains central to many later mechanical measuring instruments.