Definition
Also called magnetic declination ashore, variation is the local difference between the direction of the Earth's magnetic field and the geographic meridian. It is named East when magnetic north lies clockwise of true north and West when anticlockwise. Values range from zero near an agonic line to more than 30 degrees in some regions and towards very large values near the poles. Variation changes slowly with time, typically a few minutes of arc per year, so charted values need updating.
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