The odometer was an instrument housed in a stout leather case and strapped to the wheel of a wagon or cart to measure revolutions. The dial, which was attached to a heavy brass weight, hung down while the frame and worm gear revolved with the wheel to which it was strapped.  At night the readings were averaged and converted to miles. If the route had been level, no correction factor was applied; if the country had been rough the reading was reduced from 1 to 3 per cent.