Using a Compass

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Knowing how to use a compass allows you to do four things:

1) If you know where you are, you can use a compass to identify landmarks like peaks, passes, lakes, or ridges.

2) If you don't know where you are, you can use your map to identify the features and landmarks surrounding you, and then use compass bearings to determine your position.

3) You can use a compass to give directions to someone else. (For instance, "Follow the creek 0.2 mile upstream to the junction with four trails. Take the one that follows a bearing of 270 degrees.* Go 0.1 mile to a fence. After crossing the fence, follow a bearing of 100 degrees 200 yards cross-country to the campsite.")

4) Finally, you can use a compass to follow a directional bearing to a place that you cannot see.

There's no real difficulty in learning to use a compass. There is, however, a great deal of difficulty in describing the use of a compass to someone who is not holding one in his hand. If you read this section without a compass, it will seem hopelessly confusing. Do yourself a favor: Get a compass. Any compass.

First things first. You already know that the compass needle points north. (Which end of the compass needle should be fairly obvious: It should be distinguished in some easily visible way—red or gold paint, or with an arrow at the tip.) Next, there is the minor matter of declination. Declination—more simply expressed as the difference, in degrees, between where your compass says north is and where north really is—is the result of the fact that the earth has two North Poles. The magnetic pole, to which your compass points, is actually several hundred miles away from the geographic, or "true," North Pole. (To further complicate matters, magnetic north moves around from year to year—although not generally enough to affect the kind of navigation we are discussing in this chapter.) True north is where the northern axis pokes out of your globe at home; true north is also the frame of reference for your map. Meanwhile, your compass stubbornly points to the other, "wrong" North Pole. In order for your compass and your map to agree on which way is north, you need to make an adjustment. The amount of the adjustment—the declination—is noted on your map, and it changes from place to place.

Note: You have two choices when adjusting for declination. You can adjust for declination right at the beginning, or you can shoot your bearing using magnetic north, and then add or subtract the declination. I find the first method easier (among other things, it eliminates a whole lot of arithmetic). But either method is valid, providing that you don't forget to make the adjustment, and that you make the adjustment in the right direction. Whatever you do, be consistent! In this chapter, we adjust for declination first.

*Because a compass uses a circle as its basis for measurement, it is (like any other circle) divided into 360 degrees: 0 degrees is north, 90 degrees is east, 180 degrees is south, and 27 degrees is west.