I was interested to see that an old measurement of "chains" was still in use on the railways - mind, to some extent a mile is an old measurement if that means not metric. I looked up the origin of chains. It turns out that Edmund Gunter chose the length of 66 feet for his chain because it fitted well into area calculations. 10 square chains is one acre. It is almost 20 metres in length and in India, that is now how long a chain is. Railways fix location by distance measurement because they are linear features so as long as you know which end was the start, distance is the only coordinate needed to fix location. Best help was to realise that a cricket pitch is exactly 1 chain long. Now I can visualise it.
