Magnetic Variation

The angular difference at a location between true north and magnetic north.

Also called magnetic declination, it is named east or west according to the direction of magnetic north from true north. Charts state a value for a reference year and an annual change because the Earth’s magnetic field evolves over time and varies geographically.

Variation converts between true and magnetic directions and is distinct from deviation caused by magnetism aboard the vessel. The current charted or modelled value and its sign must be applied consistently; mnemonics should not replace understanding of the direction being converted.