1. CONVERTING BEARINGS
Before converting a grid bearing to a magnetic bearing and vice versa, there are two things you must do:
1. Update the magnetic declination on your map.
2. Draw a sketch of the norths and the bearing you are working with.
a. Draw a zero line for Grid North.
b. Plot the Magnetic North zero line east or west of Grid North depending on the declination.
c. Plot a line clockwise from the appropriate North to represent the bearing.
GRID
MAGNETIC
MAG. DECLIN.
GRID BEARING
Silver Star
OHP-1

2. CONVERTING FROM A GRID TO A MAGNETIC BEARING
When converting to a magnetic bearing, you either add or subtract the magnetic declination, also called the grid magnetic angle (GMA).
WEST IS BEST: When the GMA is west of Grid North, add it to the grid bearing.
EAST IS LEAST: When the GMA is east of Grid North, subtract it from the grid bearing.
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OHP-2

3. CONVERTING FROM GRID TO MAGNETIC
Easterly declination: Westerly declination:
GB: 3200 mils
Grid bearing: mils
GMA 385 E
GMA 420 W
Magnetic Bearing??
Magnetic Bearing??
Mag. Bearing = Grid Bearing - GMA
MB = 1600 mils mils (East is Least)
MB = 1215 mils
MB = GB + GMA (West is Best)
MB = 3200 mils mils
MB = 3620 mils
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OHP-3

4. CONVERTING FROM A MAGNETIC TO A GRID BEARING
Converting from a magnetic to a grid bearing is done in the same manner, but with a few important differences.
WEST IS LEAST: When the GMA is west of Grid North, subtract it from the magnetic bearing.
EAST IS BEST: When the GMA is east of Grid North, add it to the magnetic bearing.
Silver Star
OHP-4

5. CONVERTING FROM MAGNETIC TO GRID
Easterly declination: Westerly declination:
GMA 385 mils E
GMA 385 W
Grid Bearing??
MB mils
MB 5465 mils
Grid Bearing??
GB = MB - GMA (West is Least)
GB = 1954 mils mils
GB = 1569 mils
GB = MB + GMA (East is Best)
GB = 5465 mils mils
GB = 5850 mils
Silver Star
OHP-5