Magnetic declination, also called "magnetic variation," is the angle between magnetic North and true North on the horizontal plane. The angle is measured in minutes and degrees and is indicated by the Greek symbol delta. The angle varies with the passage of time and with changes of location on the earth's surface.Continue Reading
Magnetic North is the direction indicated by a compass when pointed towards the magnetic North Pole. True North, also called "geodetic North," is the path a meridian follows to the geographic North Pole. Magnetic declination is the angle of difference between the two. For example, in a location where the declination is 10 degrees West, true North would actually be 10 degrees East of the direction indicated by the compass.
American mathematician and author of "The New American Practical Navigator" formally defined magnetic declination as ?the angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north. The angle between magnetic and grid meridians is called grid magnetic angle, grid variation, or grivation.? A positive declination indicates that the compass is east of true North, and a negative declination indicates that it is West.Learn more about Magnetism