It is very common to always see some numbers written on the road. Sometimes, they are written on the culverts, electricity poles or just on the road itself. The writings are quite complicated that any common or layman cannot easily decipher their meanings. For instance, a writing like KM3+500.
These numbers are called Chainages in road construction or survey. Chainage refer to a distance measured in metres along an imaginary line, such as the centre line of a road or railway. In road construction, chainage is the distance from the starting point of the road to a given point.
At the starting point, the figure reprsenting the chainage will be something like KM00+000. This figure will be increasing in multiples of 20 so that at the next point it will read as KM00+020. Since road or rather distance is measured in Kilometres, the KM stands for kilometers and the number following it will show the kilometers from the starting point. The next number after the Plus sign indicates the meters but once it reaches 999, it changes to kilometers because 1000m equals to a kilometer. For example, Km2+622 means that it is 2kilometers and 622 meters from the starting point of that road.
In building or other forms of construction, chainages are also used but here, it refers to the distance from the center of the buidling.