To apply a bearing from the map using grid north to the compass in an area with 120 degrees westerly magnetic declination, what must you do?

• A. Subtract 120 degrees from the azimuth
• B. Add 120 degrees to the azimuth
• C. Rotate the compass 180 degrees
• D. Use true north instead

Answer: (B)

When applying a bearing from a map that uses grid north to a compass in an area with a magnetic declination of 120 degrees westerly, it's important to understand how declination affects the relationship between true north (or grid north) and magnetic north.

In this scenario, a westerly magnetic declination indicates that magnetic north is found to the west of true north. To correctly convert a bearing from grid north to magnetic north, you must account for this declination. Since the declination is 120 degrees west, you will essentially be moving the compass reading to align it with the actual direction as reflected on the map.

Adding 120 degrees to the azimuth accounts for the fact that you need to adjust your bearing from the grid north (true north) to the magnetic north, which is offset significantly in this case. This adjustment ensures that the compass indicates the correct direction relative to the magnetic field in that area.

Using true north directly or rotating the compass 180 degrees would not accurately reflect the navigational requirements needed to align with magnetic north, while subtracting would misalign the bearing even further from the target direction. Hence, adding the 120 degrees to the azimuth is the correct approach for accurate navigation in the specified conditions.