Magnetic forces in your boat can cause incorrect compass readings, known as magnetic deviation. To correct for magnetic deviation, you either need to remove the object causing the deviation, which could be anything from marine electronics to the screws securing the compass, or adjust your compass to account for the deviation. Luckily, Airguide marine compasses are easy to adjust. With a few turns of a screw, you can remove most, if not all, of the error.
Compare your Airguide compass against a hand-held compass at each cardinal direction. The easiest way to do this is to put the boat in a calm bay and turn the boat until you're pointing towards one of the cardinal directions. Use the hand-held compass to find the direction.
Turn your boat to point north. If your Airguide compass shows deviation from north, you need to adjust it with the compass' north-south compensator shaft, labeled "N-S." Rotate the shaft until the compass reads north. Verify north with your hand-held compass in case your boat drifted.
Turn your boat to the east. If the compass reads anything other than east, then rotate the "E-W" compensator shaft until the compass reads east.
Spin your boat to the south. If the compass reads anything other than south, you need to rotate the "N-S" compensator shaft to correct half that error. For example, if the error is 6 degrees, adjust the shaft to correct only 3 degrees.
Check the compass for west deviation by turning the boat to the west. Correct half the error with the "E-W" compensator shaft.