Gunter's Chain Survey System
A chain that made land arithmetic possible without decimals.
Origin
Devised by Edmund Gunter, Professor of Astronomy at Gresham College, around 1620.
The catch
Gunter chose 66 feet for one reason: ten square chains make exactly one acre. A surveyor could pace a field, multiply two numbers, divide by ten and have the acreage. Before that, calculating area from imperial lengths meant wrestling with 43,560 square feet.
The chain was a physical object: a hundred wrought-iron links joined by rings, with brass tags every ten links so a surveyor could read partial lengths at a glance. It stretched with use and had to be checked against a standard, which is why estate maps sometimes disagree by a few feet. Gunter’s decision to make it decimally divisible inside an imperial system was the practical stroke: he did not reform the units, he just made the arithmetic tractable. The cricket pitch is one chain, and always has been.