Measuring the distance between two places is a basic task in cartography. The earliest method was to walk and count the number of times a specific foot hit the ground—a thousand right steps, for example, made a mile (from the Latin "mille," meaning one thousand).
The Roman architect and engineer, Vitruvius (c. 75 B.C.E.-c. 15 B.C.E.), mechanized the process. Around 27 B.C.E. he devised a wheelbarrow-type device that dropped a pebble into a container every time its large wheel of known circumference rotated once. At first this was pushed along by hand, but it was soon incorporated into a chariot, the standard chariot wheel being 4feet (1.2 m) in diameter. This wheel turned 400 times in a Roman mile. Needless to say, the smoothness of the road was important. The device was described by Hero of Alexander in chapter thirty-four of his book Dioptra.
Around 300 C.E. the Chinese—some sources suggest Chang Heng—devised a similar, but more musical, instrument. Every time the road wheel of a special coach rotated once, a pin moved a tooth on an internal cog wheel. Every complete rotation of the cog wheel activated a stick that banged a drum. Every tenth drum beat was replaced by a sounding gong. Distances between towns could be easily measured in this way to an accuracy of a tenth of a mile.
Early motor cars had odometers (or mileometers) fitted to one of the road wheels, these having separate gears that registered distances of 1,10,100,1000 miles, and so on. Measured distances were a function of the tire pressure. Since 1980, cars have had odometers that indicate the number of miles traveled up to 999,999. Simple hand-pushed odometers are still used today by city surveyors, and these are sometimes called waywisers or perambulators.
