What is compass deviation?

Compass deviation refers specifically to the discrepancy introduced by magnetic fields inside the vehicle or vessel itself, which can lead to inaccuracies in navigation. When a compass points to magnetic north, it may not align perfectly due to these local magnetic influences. Thus, compass deviation is the difference between the magnetic north indicated by the compass and the true magnetic north, which is why the choice that states it is the difference between magnetic north and compass north is accurate.

This concept is crucial in navigation as it helps identify how much to adjust compass readings for accurate direction-finding and routing. Understanding compass deviation allows navigators to make the necessary allowances for precision in their navigation.