The Surveyor’s Chain
The surveyor’s or land chain was invented by Reverend Edmund Gunter in 1620. An interest in geometry led Gunter to develop a method of sea surveying that used triangulation to calculate distance. Linear measurements were taken between topographical features, for example corners of a field, and using triangulation, the field or other space could be plotted and its area calculated. A chain 66 feet long, with intermediate measurements marked, was used for this purpose. This chain became known as Gunter’s chain and the length of 66 ft. became known as a “chain”.
The chain contains 100 links, each measuring 7.92 inches. The length of the chain is equal to 4 rods, which measures 22 yards, or 66 feet. A mile is 80 chains in length. A furlong is 10 chains in length.
A legal acre contains 10 square chains, 4840 square yards, 43,560 square feet, or 100,000 square links.
Tallies or tally pins are used with a chain to mark measurements. These brass tallies have one, two, three, or four notches to mark ten, twenty, thirty or forty links from either end. A rounded tally at the fiftieth link distinguishes it from the others.
One of the earliest surveying tools was the theodolite. The first mention of the theodolite was found in the surveying text, Pantometria, written in 1571 by Thomas Digges. A theodolite is an instrument that resembles a small telescope mounted on a tripod.
The device can be used to calculate the distance from its location to a specified point. Surveyors still use this tool to measure the land today. They look through the eyepiece of the theodolite which contains mirrors and a small, etched piece of glass to measure distance and gather the information needed to triangulate the property. This device was the most widely used piece of surveying equipment for 200 years until the invention of the total station in the 1970s.