Compass Got You Lost? Adjusting for Magnetic Declination

A compass is a tried and true navigation tool, but when used incorrectly, this nifty navigator can get you horribly lost. Why is this? Your compass and your map are each using a different north.

In order to become the Magellan of your outdoor crew, you need to first understand the difference between true north and magnetic north and learn how to adjust your compass accordingly.

Magnetic Declination

True north is what is shown on the grid of a map and aligns with the earth's axis points. Magnetic north is what is shown on a compass and aligns with the earth's magnetic fields.

Magnetic Declination United States

Some maps include magnetic north along with true north, but it's important to note that since the earth's magnetic field is always changing, magnetic north changes over time. For this reason, we recommend using a trusted, up-to-date source to find magnetic declination, such as the National Oceanic and Atmospheric Administration (NOAA).

What is magnetic declination?

Magnetic declination is the difference between true north and magnetic north based on your location. Adjusting for magnetic declination is simply taking into account how far off magnetic north is from true north, and making an adjustment by either using mental math or setting your compass accordingly. This adjustment will ensure you are traveling in the right direction (and not getting hopelessly lost).

So how do you adjust for magnetic declination? Don't let this complex-sounding term throw you off; it's relatively simple.

Setting Declination for an Adjustable Compass

Adjustable compasses with adjustment screws are your best bet when it comes to magnetic declination. Just set it and forget it! Here's how:

Step 1: Using a trusted source online (like NOAA), find your local declination by entering the coordinates of where you plan to travel. This will show you how many degrees separate true north from magnetic north in your area.

Step 2: Flip the compass over and find the the adjustment screw on the back of the compass.

Step 3: Insert the key that comes with your compass into the adjustment screw and twist the key until the declination line at the bottom of the compass (the static line/box below the orienting arrow box) aligns with the declination you just learned. For example, if your magnetic north is 8 degrees east of true north, twist the screw until the declination line aligns with 8 degrees east.

That's it! Your compass is now set for this area. Continue navigating as you normally would. You will need to reset the adjustment screw according to local declination for each new area you explore.

Setting Declination for a Digital Compass

Adjusting for magnetic declination on a digital compass, such as a digital watch, is another easy way to get moving in the right direction. Adjusting for magnetic declination is dependent on the watch. Follow instructions from the watch's manufacturer to properly adjust your compass watch for magnetic declination.

Compass apps can also be downloaded onto your smartphone, whether you are an Apple or Android user. Both the Apple and Android apps allow you to easily add coordinates and toggle between true north and magnetic north, which is a huge bonus. The downside? The accuracy of these smart phone compasses is yet to be determined. Some users have noticed differences in calibration between their phone and compass, and even between several phones in the same location.

Setting Declination for a Fixed Compass

You can account for magnetic declination in non-adjustable compasses by using mental math. Instead of using a declination screw to adjust your compass, you will need to add or subtract the variance along the route and adjust your compass's bezel (the adjustable face with a directional scale) along the way.

Step 1: Using a trusted source online (like NOAA), find your local declination by entering the coordinates of where you plan to travel.

Step 2: Place the compass on the map between your starting point and your destination.

Step 3: Turn the bezel until the orienting lines are parallel with the meridian lines on the map, with N pointing north.

Step 4: Look at your bearings (the numbers on the directional scale of the bezel) and add or subtract the number of degrees necessary to compensate for magnetic declination. Adjust your bezel so it's aligned with your new bearing that accounts for magnetic declination.

Step 5: Hold the compass at waist height and turn your body so that the arrow is aligned in the orienting arrow box.

If you are using this method, you will need to adjust for magnetic declination each time you use your compass to orient yourself. Because of this, there's more room for error, which translates to a greater chance of you getting lost. We highly recommend using a compass with a declination screw for the best chance of navigating safely.

Note: If you couldn't follow the above process because your compass does not have an adjustable bezel, do not use that compass for navigational purposes.

Now that you understand what magnetic declination is and how to adjust for it on your compass, you are well on your way to being a navigation pro in the backcountry.
posted by
Lauren Seidl
Blogger at Sierra Trading Post
Lauren enjoys hiking, camping, climbing and exploring the outdoors. She's always up for trying something new, especially if it involves getting outside. When Lauren isn't out finding adventures in her home state of Colorado, she can be found writing as Sierra Trading Post's blogger.
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