Description:

This model represents a tool for calculating distances precisely. Leonardo, closely following the description given by Vitruvius in De Architectura, illustrates its mechanical features fully with an accurate drawing and analysis of them in the minutest detail.  The device has the shape of a wheelbarrow, the frame of which advances on a central wheel which touches the ground; every full turn of this wheel makes the vertical toothed wheel above it advance by one peg and, in its turn, for each full turn completed, it moves the other large central horizontal wheel, which serves as a rev. counter.  There are a series of holes along the inside edge of the horizontal wheel, to be constantly filled with pebbles or small metal or wooden balls which, every time the wheel advances by one peg, fall one at a time into the special container fitted below it. After collecting and counting the pebbles or balls, if one knows the measurement of the circumference of the wheel, it is possible to calculate the distance travelled.