magnetic declination

Magnetic declination, also called magnetic deviation (symbol D), is the amount by which the direction indicated by a magnetic compass differs from the direction of true north. It arises because the magnetic north pole is not coincident with the true North Pole. As a result, declination varies from place to place on the Earth's surface. Also, because the north magnetic pole slowly moves over time, declination varies from year to year. Angles to the east of true north are taken as positive; angles to the west are negative. See also magnetic inclination.