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Related to grid variation: agonic line
(Navigation) nautical the angle between grid north and magnetic north at a point on a map or chart. Also called: grivation
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
See: grid magnetic angle.
Dictionary of Military and Associated Terms. US Department of Defense 2005.