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A) Obtain the local magnetic declination for the area represented on your map. At the bottom of every USGS map is a diagram that displays the difference & direction between true north (represented as a star), grid north (abbreviated as "GN"), and magnetic north (abbreviated as "MN"). Magnetic declination is the number of degrees and direction between true north and magnetic north. Because declination varies over time, it is advisable to get a reasonably current figure. If your USGS map is more than 15 years old (the declination date appears in the diagram), here’s an easy-to-use website that gives you only the information you need for your specific area:
Magnetic Declination Calculator
If magnetic north is east of true north, the local declination is positive.
If magnetic north is west of true north, the local declination is negative.
B) Draw a line on the map that connects your starting point with the destination (your "map bearing"). Extend the line all the way through the map border (the "neat line").
C) Distance yourself from any nearby metal such as keys, belt buckle, desk, car, fence, etc. Place the compass on the map so the needle’s pivot point is directly over the intersection of your map bearing and neat line.
D) Rotate the dial until compass ring north agrees with map north. Read your map bearing from the compass dial. Make sure the bearing agrees with your direction of travel – for example, if you intend to travel due east, the bearing is 90 degrees, not 270 degrees.
E) Do this step mentally – don’t turn the compass dial: If the local declination is positive, then subtract the declination amount from the bearing you just derived. If the local declination is negative, then add the declination amount to the bearing you just derived.
F) Turn the compass dial until the figure you calculated in step E lines up with the index line.
G) Lift the compass off the map, and with the direction of travel arrow pointing directly away from you, rotate your body and the compass all in one motion until the red magnetic needle overlays the orienting arrow.
H) Sight a landmark along this bearing, and proceed to it. Repeat this step until you reach your destination.
