How to Determine True North

by Mark Keller

While a compass never lies, it can deceive you. The direction it tells you is north just might be wrong. Compasses point toward the magnetic north pole, located near Ellesmere island in northern Canada---but true north is about 70 miles away. Depending on where in the world you are located, the difference between where your compass is pointing and where you are in relation to true north can be considerable. But it is possible to determine true north's position very easily.

Go to the National Oceanic and Atmospheric Administration's (NOAA) online declination calculator (all links can be found under References). If you live in the United States, enter your zip code and press "Get Location" to obtain your coordinates. If not, you will have to enter your latitude and longitude manually. Click "Compute Declination" to see the declination for your location---the degree of error between true north and where your compass is pointing.

Alternately, go to the Magnetic Declination website. The site will instantly calculate your declination based on your IP address, requiring no work on your part.

If you are going to need to calculate declination in a region where you have no Internet access, purchase a declination map or print one out online (a map showing declination for all of the United States is included on the site found in the References section of this article). Note that declination maps become innaccurate after only a few years, due to the movement of the Earth's magnetic field.

If you have a compass with adjustable declination, dial in the declination variance. You will now be able to read the compass normally, but the numbers will align with true north rather than magnetic north. The point on your compass marked 0° is now true north.

If your compass does not have adjustable declination, subtract your declination from 0° to get true north. Treat easterly values as positive numbers, and westerly values as negative. Thus, if your declination is 2° West, subtract -2 from 0, which gives you +2. In this instance, when your needle is pointing at 2°, you are facing due north.

Items you will need

• Compass (preferably with adjustable declination)