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1. a unit of length, used esp in navigation, equivalent to the average length of a minute of latitude, and corresponding to a latitude of 45?, i.e. 1852 m (6076.12 ft.)
2. a former British unit of length equal to 1853.18 m (6080 ft.), which was replaced by the international nautical mile in 1970
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
nautical mile[′nȯd·ə·kəl ′mīl]
A unit of distance used principally in navigation; for practical consideration it is usually considered the length of 1 minute of any great circle of the earth, the meridian being the great circle most commonly used; the International Hydrographic Bureau in 1929 proposed a standard length of 1852 meters, which is known as the international nautical mile.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
the earth is an oblate spheroid. However, for the purpose of navigation, the International Nautical Mile of 1852 m (6076.1033 ft) has been adapted as the standard for air navigation.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved