|This is an example of a "chain" that is normally 66' long consisting of 100 links. A "chain" of 66' can also be described as being 4 poles of 16.5'.
Other tools used by a surveyor to measure distance can be a steel tape of lengths of up to 500' and the modern electronic distance measuring devices that can measure distances in excess of several miles with the use of reflector prisms.
In fact, the first men to land on the moon left behind a grouping of reflector prisms that allowed surveyors and scientists to measure the distance from the earth to the moon to an accuracy of just a couple of feet.
Invented by clergyman Edmund Gunter, the surveyor's chain made it possible to accurately measure distances and acreage in an era before global positioning satellites permitted mapping from space. The surveyor's chain made it possible for Lewis and Clark to map the Louisiana Purchase and lay out cities, townships and railroads. Here's an explanation of the measurements and how to use them.
Equate a standard surveyor's chain, or Gunter's chain, to 66 feet or 22 yards. There are also half-length chains of 33 feet. Equate an engineer's chain, or Ramsden's chain, to 100 feet.
Divide a surveyor's chain into 100 links, equal to 0.66 feet, or 7.92 inches. Gunter's original chain was made with 100 links, a half-chain with 50. A Pennsylvania surveyor's chain, while 66 feet long, is made with only 80 links.
Convert a measurement in surveyor's chains into rods by multiplying by 4, into furlongs by dividing by 10 and into miles by dividing by 80. Convert a length in surveyor's chains to meters by multiplying by 20.1168 and into kilometers by multiplying by 0.0201.
Tips and Warnings
An acre of land is equal to 10 square chains. A square mile is equal to 640 acres or 6,400 square chains (80 chains on each side, 80 x 80 = 6,400).
By 1785 law, only Gunter's 66-foot chain was allowed for land surveying work.