Magnetic to compass conversion uses which equation?

• A. True ± Variation = Magnetic
• B. Magnetic ± Deviation = Compass
• C. Variation + Deviation = Compass error
• D. Lining up objects to check position

Answer: (B)

Magnetic to compass conversion is about correcting the magnetic heading with the compass deviation to get what the compass would actually read. The direct relationship is compass heading equals magnetic heading plus or minus the deviation, with the sign chosen based on the direction of the deviation (east adds, west subtracts). That’s why the statement Magnetic ± Deviation = Compass is the correct way to express this conversion. In practice, you’d go True to Magnetic by applying variation (True ± Variation = Magnetic), then Magnetic to Compass by applying deviation (Magnetic ± Deviation = Compass). For a quick check: if the magnetic heading is 120 degrees and the deviation is 4 degrees east, the compass would read 124 degrees; if the deviation is 4 degrees west, it would read 116 degrees. The other options either describe a True-to-Magnetic step, mix concepts, or refer to something irrelevant like lining up objects.