What is magnetic variation?
The compass rose on the boating safety chart shows both the direction of true north and magnetic north. True north always points along the meridian of longitude towards the true north pole. Magnetic north points to the current position of the magnetic north pole. The difference between true and magnetic north is the ‘magnetic variation’. The magnetic north pole revolves very slowly around the true north pole. Therefore, the magnetic variation changes slowly on charts, and can go from positive to negative to positive again over a very long period. See the notes in the title area on boating safety charts for applying the variation to courses set by compass.
