The angle between the direction a compass needle points at a given location and the direction of true north.
The horizontal angular difference between True North and Magnetic North.
The angle between magnetic north and geographical north at a given place.
The phenomenon of the earth's magnetic field not being in the same place as true north or grid north; thus, to convert a bearing taken from a magnetic compass, to a bearing able to be used on a map grid (or vice versa), you need to correct for magnetic declination. The exact amount of correction needed is usually found on the margin of your map
The angle between magnetic north and true north, expressed in degrees and minutes, east or west from true north.
The angular difference between observed magnetic North on a compass and geographic or "true" North. Magnetic declination is not constant--rather, it varies annually due to the "wandering" of the North Pole.
(Magnetic Variation) In most places compasses do not point to True North they will point toward Magnetic North. The difference between True North and Magnetic North is the Magnetic Declination. The magnetic North Pole moves slowly therefore the magnetic declination changes slowly from year to year, but not enough to be of concern for our purposes. For example at present the change in the contiguous 48 states varies from a minimum of 5’ (minutes) E or W per year (meaning it'll take 12 years to change the declination by one degree) to a maximum of 12° W (meaning it changes one degree in five years). Hawaii, where the declination is 11°E to 12°E, has virtually no annual change now. (Sailors use the term “variation” for Magnetic Declination.) Allowing for Declination: If your Preferences have been set for Magnetic North, all the calculations made by the program will make the necessary adjustments for the magnetic declination. This allows you to take direct reading with your compass without any compensation. If you select True North in the Preferences, you must make declination corrections on your compass for a true reading.
() the difference in degrees between magnetic north and true (geographic) north
The difference between True North and the direction that a magnetic compass points for a given location. Magnetic declination varies from place to place and can change as much as a degree in a year.
The angle between the magnetic and geographical meridians at any place expressed in degrees, east or west, to indicate the direction of magnetic north from true north.
The horizontal angle between true north and magnetic north or true south and magnetic south.
The angle of divergence between true north and magnetic north. Measured in degrees east or west of true, or geographic north.
The magnetic declination at any point on the Earth is the angle between the local magnetic field -- the direction the north end of a compass points -- and true north. The declination is positive when the magnetic north is east of true north. The term magnetic variation is equivalent, and is more often used in aeronautical and other forms of navigation.