How to Read a Compass

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121222222Navigation by way of compass may seem daunting at first to a beginner, but this trepidation shouldn’t stand in the way of learning to use one. In fact, once you learn how to read a compass, it will be a valued friend in the back-country — one you can always count on to help guide your steps.

This guide is meant to be a general overview of the basics of learning how to read a compass, with or without a map. There are only a few key things to keep in mind, and once you have grasped these fundamentals, the realm of compass navigation will be open to you forever.

Compass Basics

First of all, what exactly does a compass do? In short, a compass is a fixed housing containing a free-floating metal “compass needle” able to align itself to the Earth’s magnetic field. One end of the compass needle will always point towards the north magnetic pole. An important fact to mention here is that magnetic north is not the same as geographic north. A map will make reference to geographic north, i.e. the North Pole, a fixed point on the Earth’s surface, whereas magnetic north fluctuates in position over time. This is known as magnetic declination. I’ll come back to this in a moment.

In addition to the floating compass needle, a compass may have a myriad of other features, but only a few are really relevant to basic orienteering. The first, and most important, is the rotating bezel on the face. The bezel contains the 360 degrees of a circle, or the azimuth. Another often-used term is bearing. So the bezel allows the user to “dial-in” his or her desired direction of travel simply by rotating the face.

Let’s say for example that you know your home base is in a southeasterly direction, ~120 degrees of azimuth. If you wanted to make sure you traveled in that direction, you would first orient yourself so that the red (north) end of the compass needle is aligned with the N (0°) mark on the bezel. Next, you would rotate the bezel until the needle pointed to 120°. Finally, you would simply rotate yourself so that the needle once again pointed to the N (0°) mark. And voila, you now have your bearing – a key piece of learning how to read a compass.

Magnetic north or Geographic north?

There is one catch, though. Remember what I said about magnetic north not being true or geographic north? Well, the difference between the two is determined by your location on the Earth’s surface, and it’s enough to really throw off your bearing and put you into the nearest swamp. Luckily, the bezel holds the key once again. Once you know your magnetic declination, you simply rotate the bezel according to that number. For instance, let’s pretend you live in Seattle, and know your magnetic declination to be 16° 51′ E. In this case, the difference of magnetic north is ~ +17° from true north, so we need to subtract that from our current bearing by rotating the bezel to the right. So with our compass needle now pointing north again, our housing (and thus our direction of travel) will be oriented to 343°. Confused? Not surprising. But take heart, it is much easier to understand once you have your compass in hand. (Note: If you need help determining your magnetic declination, NOAA offers this handy tool.)

How to Choose a Compass

Finally, you might be asking, “How do I choose the right compass for me?” While there are lots of compass models on the market, the best ones will not be overwhelming with features nor so bare bones that they lack even a rotating bezel. My personal recommendation is to go with a standard, liquid-filled orienteering compass such as that made by Suunto or Brunton. Stay away from “button” compasses or those found in the hilts of knives. They are largely inaccurate and will not help you in the long run. Once you grasp the basics of learning how to read a compass, you can graduate to one with more advanced features. That being said, as long as your compass has a rotating bezel and can reliably point to magnetic north, you have everything you need to find your way. And will just a little practice, you’ll be amazed how easily you can do just that.

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