How is magnetic deviation corrected on a vessel?

• A. Using a deviation table.
• B. By adjusting the compass until it points true north.
• C. By recalibrating variation using astronomic observations.
• D. By increasing ballast to shift the compass.

Answer: (A)

Magnetic deviation is the local magnetic interference caused by the ship itself affecting the compass readings. The standard way to correct for this is to use a deviation table. During a deviation survey, the ship’s compass readings are recorded on many headings, and the deviations (in degrees) are compiled into a table. This table lets you convert what the compass shows into a true or magnetic course as needed, compensating for the ship’s unique magnetic field on each heading.

Why this is the best approach: it directly accounts for the vessel’s specific interference at sea and provides a practical correction for every heading the navigator might use.

Adjusting the compass until it points true north would ignore the ship’s internal magnetic field and isn’t how sailors achieve accurate steering. Recalibrating variation with astronomic observations addresses variation—the difference between true north and magnetic north at a location—not the ship’s local deviation. And increasing ballast to shift the compass isn’t a reliable or standard method for correcting deviation.