Gunter's chain, c.1880 (iron & brass)

A Gunter’s chain measures the distance of 1 chain or 22 yards, the distance between the wickets on a cricket pitch, and is named after its creator, Edmund Gunter (1581–1626), Professor of Astronomy at Gresham’s College, London, and a mathematician, who designed his chain in the 1620s for land measurement. Gunter’s chain comprises a hundred links marked off into groups of ten by brass tags. A circular tag marks the half chain and a further two sets of tags (of one, two, three and four teeth) mark the remaining eight decimal graduations. Rectangular areas of land can be computed by measuring two adjacent sides using Gunter’s chain. The product of the two lengths can be converted to acres by dividing by ten since there are 10 square chains in an acre. For example, a rectangular plot of land measures 7.5 chains by 25 chains: the area is 187.5 square chains or 18.75 acres. Although designed primarily for pioneering map-making, designation of land holdings and for urban planning, it was used extensively for surveying irregular areas by normal triangulation methods.1 Gunter’s chain was fundamental in the surveying of the eastern United States and, from 1785, the grid that formed the basis for city blocks. In 1829, James Chesterman, the founder of the firm which made this Gunter’s chain, patented the spring tape measure. His firm was amalgamated with John Rabone & Sons in 1963 and was taken over by Stanley Tools Ltd in 1990.