Chaîne d'arpenteur

Gunter's chain (also known as Gunter's measurement) is a distance measuring device used for surveying. It was designed and introduced in 1620 by English clergyman and mathematician Edmund Gunter (1581–1626). It enabled plots of land to be accurately surveyed and plotted, for legal and commercial purposes. Gunter developed an actual measuring chain of 100 links. These, the chain and the link, became statutory measures in England and subsequently the British Empire. The chain is divided into 100 links, usually marked off into groups of 10 by brass rings or tags which simplify intermediate measurement. Each link is thus long. A quarter chain, or 25 links, measures and thus measures a rod (or pole). Ten chains measure a furlong and 80 chains measure a statute mile. Gunter's chain reconciled two seemingly incompatible systems: the traditional English land measurements, based on the number four, and decimals based on the number 10. Since an acre measured 10 square chains in Gunter's system, the entire process of land area measurement could be computed using measurements in chains, and then converted to acres by dividing the results by 10. Hence 10 chains by 10 chains (100 square chains) equals 10 acres, 5 chains by 5 chains (25 square chains) equals 2.5 acres. By the 1670s the chain and the link had become statutory units of measurement in England. a Word or two of Dimensurators or Measuring Instruments, whereof the mosts usual has been the Chain, and the common length for English Measures 4 Poles, as answering indifferently to the Englishs Mile and Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square Mile contains 640 square Acres...' The method of surveying a field or other parcel of land with Gunter's chain is to first determine corners and other significant locations, and then to measure the distance between them, taking two points at a time. The surveyor is assisted by a chainman. A ranging rod (usually a prominently coloured wooden pole) is placed in the ground at the destination point.