magnetic declination

Also known as magnetic variation, variation, declination, northeasting of the needle

angle on the horizontal plane between magnetic north and true north

~18 min read

Encyclopedic overview

Example of magnetic declination showing a compass needle with a "positive" (or "easterly") variation from geographic north. Ng is geographic or true north, Nm is magnetic north, and δ is magnetic declination.

Magnetic declination (also called magnetic variation) is the angle between magnetic north and true north at a particular location on the Earth's surface. The angle can change over time due to polar wandering.

Excerpted from Wikipedia’s “magnetic declination” article, available under the CC BY-SA 4.0 licence.