In 1620 an English mathematician and astronomer named Edmund Gunter described a surveyor's chain with 100 links, measuring 66 feet (22 yards or 4 poles) overall. By this design, one square chain equals 484 square yards, ten square chains equal an acre, and eighty chains equal a mile. Gunther's design proved extremely popular, especially in English lands. This example belonged to John Johnson (1771-1841), the Surveyor General of Vermont. It is made of steel, with round handles at either end, brass tallies every 10 links, and swivels every 25 links. Each link is joined to the next by three rings, and each unit (link and three rings) is 7.92 inches long.