Odometer in the context of Zero milepost

Kilometre zero (or km 0), also known as zero mile marker or zero milepost, is a particular location (usually in the nation's capital city) from which traveled distances are traditionally measured, as in distance markers. Historically, they were markers where drivers could set their odometers to follow the directions in early roaming guidebooks.

One such marker is the Milliarium Aureum ("Golden Milestone") of the Roman Empire, believed to be the origin for the maxim "All roads lead to Rome".

The chain (abbreviated ch) is a unit of length equal to 66 feet (22 yards), used in both the US customary and Imperial unit systems. It is subdivided into 100 links. There are 10 chains in a furlong, and 80 chains in one statute mile. In metric terms, it is 20.1168 m long. By extension, chainage (running distance) is the distance along a curved or straight survey line from a fixed commencing point, as given by an odometer.

The chain has been used since the early 17th century in England, and was taken by British settlers during the colonial period to other countries around the globe. In the United Kingdom, there were 80 chains to the mile, but until the early nineteenth century the Scottish and Irish customary miles were longer than the statute mile; consequently a Scots chain was about 74 (imperial) feet, an Irish chain 84 feet. These longer chains became obsolete following the adoption of the imperial system of units in 1824. In India, "metric chains" of exactly 20 metres (65.62 feet) are used, along with fractions thereof.

An adding machine is a class of mechanical calculator, usually specialized for bookkeeping calculations. Consequently, the earliest adding machines were often designed to read in particular currencies. Adding machines were ubiquitous office equipment in developed countries for most of the twentieth century.

They were phased out in favor of electronic calculators in the 1970s and by personal computers beginning in about 1985.

Mechanical counters are counters built using mechanical components. They typically consist of a series of disks mounted on an axle, with the digits zero through nine marked on their edge. The right most disk moves one increment with each event. Each disk except the left-most has a protrusion that, after the completion of one revolution, moves the next disk to the left one increment. Such counters have been used as odometers for bicycles and cars and in tape recorders and fuel dispensers and to control manufacturing processes. One of the largest manufacturers was the Veeder-Root company, and their name was often used for this type of counter. Mechanical counters can be made into electromechanical counters, that count electrical impulses, by adding a small solenoid.