Leonardo da Vinci’s odometer measured distance by counting the rotations of a wheel.
His design used a cart with a wheel connected to a gear mechanism. As the wheel turned, the mechanism moved a set of counting wheels. A container could release a small object, such as a stone, at regular intervals, allowing the operator to count the measured units along a route.
Leonardo’s odometer was intended for surveying and mapping. It did not display distance with an electronic screen, and its accuracy depended on the wheel’s size, the gear ratios, and the condition of the ground. Those limitations were normal for mechanical measuring instruments of the period.
The basic principle remains familiar in modern odometers: rotation is converted into a distance reading using a known circumference. Leonardo’s invention is distinct from a pedometer, which counts steps, and from an anemometer, which measures wind speed.