Odometer
This machine, known since antiquity, is for measuring distance traversed.
Leonardo's odometer looks like a wheelbarrow provided with sprocket
wheels. The vertical wheel takes a step with every turn of the hub of
the wheel that rests on the ground. The vertical sprocket wheel has
on the inside a peg which, at every full revolution, meshes with the
horizontal wheel. The latter is provided with holes through which small
metal balls or stones are collected into a dedicated holder. The distance
traversed can be easily inferred by counting the balls/stones collected.
Codex Atlanticus, sheet 1a