Which equation defines compass error as the sum of variation and deviation?

• A. True ± Variation = Magnetic
• B. Magnetic ± Deviation = Compass
• C. Variation + Deviation = Compass error
• D. Line formed by two objects

Answer: (C)

Compass error comes from two separate sources: variation, the difference between true north and magnetic north at a location, and deviation, the error introduced by the ship’s own magnetic field. Each of these factors shifts the compass reading away from the true heading, and their effects add together to produce the total compass error. That’s why the correct relationship is Variation plus Deviation equals Compass error. In practice, you determine variation from charts and deviation from compass calibration, then combine them to understand the overall error you must correct for on the water. The other formulations mix the quantities improperly or refer to unrelated ideas, so they don’t describe how compass error is formed.