Gunter's chain, 19th century.
© Science Museum / Science & Society Picture Library
Surveyor's chain made by Baker in the 19th century. Ropes, chains, tapes and rods have all been used for measuring distances. In about 1620, English mathematician and astronomer Edmund Gunter (1581-1626) developed this type of metal chain for determining the area of plots of land. The chain is 20 metres (66 feet) long, and is made of 100 links. Markers are placed at regular intervals.