Use of the inch can be traced back as far as the 7th century. The first explicit definition we could find of its length was after 1066 when it was defined as the length of three barleycorns. This was not a satisfactory reference as barleycorn lengths vary naturally. The British Standards Institute defined the inch as 25.4mm in 1930 in the document "Metric Units in Engineering: Going SI". In March 1932 the American Standards Association were asked to rule on whether to adopt the same value (at the time the American inch was 1/.03937 mm which approximated to 25.400051 mm). Because the values were so close, and because Britain has already settled on that value, the ASA adopted this value on March 13, 1933.
Inches to Chains
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Unit of length equal to 66 feet, used especially in the U.S. public land surveys. The original measuring instrument (Gunter's chain) was literally a chain consisting of 100 iron links, each 7.92 inches long. Steel-ribbon tapes began to supersede chains around 1900, but surveying tapes are often still called "chains" and measuring with a tape is often called "chaining". The chain is a convenient unit in cadastral surveys because 10 square chains equal 1 acre.