How do you compute a true bearing from a magnetic bearing when you know the local magnetic declination?

• A. Subtract the declination from magnetic bearing if east; add if west.
• B. Always add the declination to magnetic bearing.
• C. Add the declination to the magnetic bearing if the declination is east; subtract if it is west.
• D. Never adjust for declination.

Answer: (C)

Magnetic declination tells you how far magnetic north is from true north. A true bearing is relative to true north, while a magnetic bearing is relative to magnetic north. To get the true bearing, you adjust the magnetic bearing by the local declination.

If the declination is east, you add it to the magnetic bearing because magnetic north is east of true north, so the true bearing will be larger. If the declination is west, you subtract it because magnetic north is west of true north, making the true bearing smaller.

Examples help: magnetic bearing 030 with east declination 12° → true bearing 042°. Magnetic bearing 030 with west declination 12° → true bearing 018°.

So the correct approach is to add for east declination and subtract for west declination.