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When plotting a course, some small aircraft pilots may plot a trip using true north on a sectional chart (map), then convert the true north bearings to magnetic north for in-plane navigation using the magnetic compass. These bearings are then converted on a pre-flight plan by adding or subtracting the local variation displayed on a sectional chart.
In surveying, bearings can be referenced to true north, magnetic north, grid north (the Y axis of a map projection), or a previous map, which is often a historical magnetic north. [citation needed] If navigating by gyrocompass, the reference direction is true north, in which case the terms true bearing and geodetic bearing are used.
1 - True North 2 - Heading, the direction the vessel is "pointing towards" 3 - Magnetic north, which differs from true north by the magnetic variation. 4 - Compass north, including a two-part error; the magnetic variation (6) and the ship's own magnetic field (5) 5 - Magnetic deviation, caused by vessel's magnetic field.
3 – Magnetic north, which differs from true north by the magnetic variation. 4 – Compass north, including a two-part error; the magnetic variation (6) and the ship's own magnetic field (5) 5 – Magnetic deviation, caused by vessel's magnetic field. 6 – Magnetic variation, caused by variations in Earth's magnetic field.
Again, if one is using "true" or map bearings, and the compass does not have preset, pre-adjusted declination, one must additionally add or subtract magnetic declination to convert the magnetic bearing into a true bearing. The exact value of the magnetic declination is place-dependent and varies over time, though declination is frequently given ...
Compass needles in the Northern Hemisphere point toward the magnetic North Pole, although the exact location of it changes from time to time as the contours of Earth’s magnetic field also change.
According to FAA, it is the angle between true north and magnetic north. Direction compass points is not magnetic north, because bearing of compass is affected not only by the local magnetic variation but the carrier's own magnetic field as well. —The preceding unsigned comment was added by Natasha2006 (talk • contribs) 18:40, 25 April 2007 ...
An azimuth compass (or azimuthal compass) is a nautical instrument used to measure the magnetic azimuth, the angle of the arc on the horizon between the direction of the Sun or some other celestial object and the magnetic north. This can be compared to the true azimuth obtained by astronomical observation to determine the magnetic declination ...