Gunter's chain n.
Surveying a measuring instrument 66 ft (20.1 m) long, subdivided into 100 links (1 rod or perch = 25 links), each link being a short section of wire connected to the next link by a loop. It was long used for land surveying and became a unit of length (80 chains = 1 mile), but has now been superseded by the steel tape and electronic equipment. [Edmund Gunter, Engl. mathematician (1581-1626)]

—The Oxford English Reference Dictionary


Gunter's Chain is the most widely known unit of measurement that is universally attributed to the Art of Surveying. It came into common usage about 1700 a.d. and was the standard for measuring distances over 150 years. Until early in the 20th Century, it was universally made of iron or brass links. Because all of these chains were hand made, they rarely measured exactly the proscribed sixty six feet in length. Thus, the surveyor had to use a correction factor when translating his notes into a drawing. In later years, it became the Surveyor's Tape that was machine made and used sophisticated metallurgy to compensate for the small (but measurable) effect of temperature on the length of the tape. These chains are commonly found in both the full (100 link) and half (50 link) lengths.