The counting device Leonardo da Vinci sketched for recording a cart’s traveled distance was an odometer.
Leonardo’s design used a cart wheel connected to a geared mechanism. As the wheel turned, the mechanism moved a series of numbered indicators or containers, allowing the operator to calculate distance from the wheel’s rotations. The concept adapted mechanical counting to surveying and road measurement.
An odometer measures distance, whereas a speedometer measures speed. Leonardo’s device was also not a modern automobile instrument: it was a manually propelled cart with mechanical components intended to record progress over ground.
Odometers existed in earlier forms, including ancient measuring devices associated with engineers such as Vitruvius and Hero of Alexandria. Leonardo’s importance lies in his detailed Renaissance study and refinement of mechanical measurement, not in inventing the general idea from nothing.