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.
A unit of length used in marine navigation that is equal to a minute of arc of a great circle on a sphere. One international nautical mile is equivalent to 1,852 meters or 1.151 statue miles. Please not that this is different to a UK Nautical mile.