Odometer (distance-measuring device)

The model represents a device designed to measure distances with precision.
Following Vitruvius’ description in the De Architectura, Leonardo accurately illustrates its mechanical features, providing a well-structured graphical representation and analysing every single detail.

The machine has the shape of a wheelbarrow: its frame is supported by a central wheel resting on the ground. Each revolution of the wheel’s hub causes a vertical toothed wheel to move one notch forward; in turn, every full rotation of this vertical gear drives another large horizontal central wheel that functions as a counter.

Along the inner edge of the horizontal wheel are several holes, which are gradually filled with small stones or little metal or wooden spheres. At each movement of the wheel, one of these drops into a special container placed underneath.

By collecting and counting the stones or spheres, and knowing the circumference of the main wheel, it is then possible to calculate the distance travelled.