model of an Odometer that Leonardo da Vinci drew on the first folio of his Codex Atlanticus, folio 1 r. 1504. This is a machine calculated distance travelled. This machine, however, was already known in antiquity, given that Leonardo did nothing more than re-elaborate the Odometer devised by Heron Alexandrinus, a Greek inventor who lived in the First century AD. Unlike the former one, the Odometer that Leonardo designed was shaped a little like a push cart and had a toothed wheel mechanism. Each time the wheel on die ground turned, the vertical toothed wheel turned once, in turn actuating a horizontal wheel. The latter contained metal balls or stones, which fell through a hole into a bucket: counting them at the end of the journey allowed the distance travelled to be calculated.