Magnetic North is the direction of the horizontal component
of the earth's magnetic field. Except near the poles, this direction
is approximately true north. The angle between the direction of local
Magnetic North and True North is called variation (also declination).
It varies from place to place and also slowly in time, and is charted
on both VFR and IFR navigation charts. ``East'' variation means that magnetic North lies to the East of true North, so that directions are related by:
The fact that even ideal magnetic compasses reference direction to magnetic North should not be thought of an error. Nevertheless it needs to be accounted for if one is interested in obtaining true headings.