Leonardo da Vinci’s odometer used a toothed wheel to measure distance traveled.
Leonardo sketched an odometer-like device in which a wheel moved along the ground and transferred motion through gears. As the wheel turned, the mechanism could count rotations and record the distance covered.
An odometer does not measure distance directly with a ruler. It uses a known wheel circumference: each complete rotation corresponds to one wheel circumference, and a gear system can convert those rotations into a count or display. Leonardo applied this principle to surveying and route measurement.
The general idea of measuring travel with a rotating wheel is much older than Leonardo. His contribution was to document a compact mechanical arrangement that connected wheel motion to counting, an approach still used in many vehicle odometers.