Which factor causes magnetic compass deviation on a vessel?

Which factor causes magnetic compass deviation on a vessel?

• A. Variation
• B. Deviation
• C. Calibration
• D. Correction

Answer: (B)

Deviation is the distortion of the compass reading caused by the ship’s own magnetic field. The vessel’s iron and steel structures, ballast, propulsion, and electrical equipment create local magnetic forces that tug the compass needle away from magnetic north. This interference changes with the ship’s heading and conditions, so each vessel often has a deviation table to apply corrections on different courses. Variation, by comparison, is the difference between magnetic north and true north caused by Earth’s magnetic field, not by the ship. Calibration and correction describe processes for figuring out and applying those adjustments, respectively, but they are not the factor causing the deviation itself. So the factor described here is deviation.

Deviation is the distortion of the compass reading caused by the ship’s own magnetic field. The vessel’s iron and steel structures, ballast, propulsion, and electrical equipment create local magnetic forces that tug the compass needle away from magnetic north. This interference changes with the ship’s heading and conditions, so each vessel often has a deviation table to apply corrections on different courses.

Variation, by comparison, is the difference between magnetic north and true north caused by Earth’s magnetic field, not by the ship. Calibration and correction describe processes for figuring out and applying those adjustments, respectively, but they are not the factor causing the deviation itself. So the factor described here is deviation.