Gunter’s chain—Invented by the English astronomer Edmund Gunter about 1620, this measuring device became the basis for the chain and link units of length used in surveying the public lands of the United States. The 66-feet-long Gunter’s chain is divided into 100 links, each 7.92 inches long. (Early chains were 50 links, or 33 feet in length.) In its earliest construction, the chain was made from iron (later, heavy steel wire), in short pieces which were bent at the end to form rings. Three extra rings were placed between the pieces, each assembly to make up one whole link, or 7.92 inches. The original form of the chain was replaced by metallic tapes or ribbons graduated in links and chains in the early part of the nineteenth century, but the new forms are still called “chains.” The chain is a convenient length for land measurement because 10 square chains equals 1 acre. See also link (definition 2).

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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