Declination

Declination is the difference between magnetic North as reported by a compass and true North.

Declination varies based upon your location on the Earth and they also change slowly as the magnetic poles of the Earth shift.

Knowing your declination is critical to being able to successfully point a satellite antenna.

Declination is expressed as a degree of angle.

If you have a West declination, you must subtract it from your compass reading to determine the true azimuth. If you have a East declination, you must add it to your compass reading to determine the true azimuth.