Suppose you’re on the east or west coast of the U.S., or somewhere else where a compass won’t point to true north. It’s dark. You’re tired. You’re trying to navigate your way to a safe location using map and compass. This is no time to be trying to do mental math every time you check a compass heading. What you really want right now is to know how to set the declination on your compass so you can just follow the nice arrow.
This post will help you learn how.
Wait, what’s this about your compass not pointing north?!? If you don’t know what declination is or how to find it for a particular area, this post will help you. Read that first and this one will make much more sense. I’ll wait.
There, that’s better, isn’t it? I’ve got three methods to share to set the declination on a compass. The first two apply to the two most popular compass makers. The third is a jury-rig for a low-end compass that doesn’t have an adjustment mechanism but does have a rotating bezel.
Getting the terms straight
Well, I can’t describe how to set a declination without nouns. Here’s a picture of the compass I have. It’s a Brunton TruArc3; lists at about $17. It’s about midline in the world of compasses, with adjustable declination but lacking other nifty features like a mirror. I’m happy with it but there are plenty of good compasses. I’m not trying to sell you anything.
A midrange compass, with adjustable declination.
The basic design of this kind of compass has three moving parts set on a baseplate.
The baseplate is the clear acrylic plate with rulers on each side and a roughly rectangular shape that forms the base. It has a long black direction of travel arrow running down its midline. In this photo the direction of travel arrow is pointing down and to the left. The point where the Direction of Travel arrow meets the bezel is the index point.
The bezel is the big black ring with all the numbers (degree markings). It rotates on top of the baseplate.
The declination adjustment disc is set within the bezel. It’s the yellow ring in this photo. It will actually rotate inside the bezel and is key to, you guessed it, set the declination. The bottom of this clear disc bears an orientation arrow. It’s a little difficult to see in this photo because the orientation arrow is an outline in the shape of the magnetic needle, and in this photo the needle is oriented right over that arrow. That’s often where the needle belongs when using the compass.
The magnetic needle is setting in the fluid-filled center of the declination adjustment disc. The magnetic needle’s red end is the one that will point north(ish).
Set the declination on a Brunton compass
Once you’ve checked the bottom of your topo map to find the declination area (or looked it up at http://www.magnetic-declination.com/), you want to set it into your compass. Then you don’t have to remember any add this/subtract that stuff while you’re trying to navigate.
To set the declination, pinch the center axis of the compass (above and below) very tightly with thumb and forefinger. Hold the rotating bezel still and rotate the declination disc until the orientation arrow (whose axis you have pinched) points to the correct number of degrees in the correct direction on the marked declination scale. For example, if your location’s magnetic declination is 10 degrees east, rotate the orientation arrow clockwise until it pointed at the 10 tic..
The first time you go to rotate your declination adjustment disc it may be a bit stiff (mine was). It never gets Really easy to turn, but that’s a good thing. Shifting by accident is not good. In fact, check it now and again to make sure it’s where it belongs.
Set the declination on a Suunto compass
I don’t like that the Suunto approach requires an extra part to set the declination. On the other hand, the little key that’s required is usually attached to the lanyard that comes with the compass. Also an upside, once set it’s not likely to shift until you do it on purpose.
Turn the compass over. On the underside at about where the yellow ring of the declination disc is on the Brunton photo there’s a ring with a little screw set in it. Take the little key that’s attached to the lanyard. Use it to turn the screw until the direction of travel arrow moves the correct number of degrees east or west on the little red scale just underneath the ends of the arrow. Done.
This is a Suunto model. The red outline is the orientation arrow. The red scale inside of the black ring is the declination adjustment scale. The orientation arrow moves along that scale when the screw in the back is turned.
Click here for a video of it.
Set the declination when the compass isn’t adjustable
What if your compass is a low-end model with no declination adjustment? Well, this tip is a little low-rent, but it sounded pretty genius to me. You still need a compass with a rotating bezel that’s clear so you can see the underside of the area under the magnetic needle.
Find your local declination as usual. Cut a thin piece of tape that will reach from the axis of your magnetic needle almost to the numbers on the bezel. Make sure to cut the end of the tape into an arrow shape. Place the tape so it runs from the axis to point at the local declination value.
Now when you’re using the compass, instead of using the supplied orientation arrow, use that piece of tape as the orientation arrow. There will be more posts in this series that talk about using the orientation arrow.
Bonus tip: Set the declination from mid-America
This one’s my favorite, because I live here. If you live near a line that runs along the eastern edge of Louisiana/Arkansas/Missouri/Iowa/Minnesota/Manitoba, do nothing. You’re done. The declination is near zero along this line. (Ok, you should check to make sure your compass isn’t set for the east or west coasts of the continent, by seeing that the orientation arrow does point at zero on the declination scale.)