Application of deviation 1

The difference between the direction of Magnetic North and the direction that the compass points to is known as Magnetic Deviation.
Compass deviation is caused by the environmental influences on your compass. On the boat, it can be influenced by electrical equipment, metal objects and magnetic fields.
Large errors can occur on westerly and easterly courses, while there may be little or no error on northerly or southerly courses.
Deviation varies at each compass point.
If compass deviation on your boat exists, it is important to create a Deviation Card.
The card provides the data needed for course correction. On any course, the deviation should not exceed 6 degrees; otherwise you should have a compass adjuster to install corrector magnets.