3D model
Author: Multimedia Laboratory of the Istituto e Museo di Storia della Scienza, Florence
Date: 1999

Odometer 3D

Forerunner of the modern speedometer, this device was connected to the wheel of a cart. It had a series of cogs which, with every turn of the wheel, caused a vertical blade to click.
At the end of every complete revolution of the blade, a horizontal wheel is released, allowing a pebble to drop into a container below.
The system was calibrated so that a pebble fell after each Roman mile.