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Magnetic Declination
Magnetic declination (sometimes called magnetic variation) is the angle between magnetic north and true north. Declination is positive when this angle is east of true north and negative when it is west. Magnetic declination changes over time, and with location. Declination value is needed to determine true north, because compasses point toward magnetic north.
Common Questions
How do I correct my compass to the true bearing?
You can compute the true bearing from a magnetic bearing by adding the magnetic declination to the magnetic bearing. This works as long as you follow the convention that degrees west are negative (i.e. a magnetic declination of 10-degrees west is -10 and bearing of 45-degrees west is -45). Some example case illustrations are provided for an east magnetic declination and a west magnetic declination.
Does the compass needle point toward the magnetic pole?
No. The compass points in the directions of the horizontal component of the magnetic field where the compass is located, and not to any single point.
Access Tools
CrowdMag
A mobile app with a digital compass that can calculate the magnetic field in your area.
Geomagnetic Calculators
Geomagnetic Calculators can be used to measure different aspects of the magnetic field for specific time frames and coordinates.