Variation
F5. The Reference Layer: Glossary, Units, Signals and Information SourcesDefinition
See magnetic variation; difference between true and magnetic north.
Variation (magnetic declination) is the angle between true north and magnetic north at a place, east or west, caused by the offset of the geomagnetic pole from the geographic pole. It is printed inside the chart’s compass rose with the year and the annual rate of change, since the field drifts. To convert a magnetic course or bearing to true, apply variation; west is least (subtract going magnetic to true), east is best (add). Variation is a property of location; deviation is a property of the individual ship.