دیکشنری تخصصی مهندسی نفت - نسخه آنلاین

n: a map that shows the isogonic lines joining points of magnetic declination, which is the variation between magnetic north and true north. For example, in Los Angeles, California, when the compass needle is pointing toward north, true north actually lies 150 east of magnetic north. See declination.

n: an imaginary line on a map that joins places on the earths surface at which the variation of a magnetic compass needle from true north is the same. This variation, which may range from 0 to 30 or more degrees either east or west of true north, must be compensated for to obtain an accurate reading of direction.