True North and Magnetic Declination: A Trick to Get You to Stick
Magnetic declination is an essential principle to understand when navigating through nature with a map and compass.
However, it is somewhat difficult to remember, at least in the way it has been traditionally taught, using an addition / subtraction method. Just when you think you’ve got it, the concept floats away, like mist in the morning light.
Well, there is a simple and practical approach to adjusting the magnetic declination when orienting yourself. The entire explanation begins with a definition of “north.”
There are 2 North
Many people know that there are two norths in terms of maps and compasses. A map shows true north, or geographic north pole, where all lines of longitude meet. The earth revolves around an imaginary axis that runs through the north and south poles.
A compass needle points to magnetic north, which is determined by the earth’s magnetic field. The location of magnetic north moves over time, at about 5 miles per hour. Right now, it’s crawling slowly somewhere NW of Hudson Bay in Canada, about 450 miles from true north.
Magnetic declination
The angular difference between true north and magnetic north is known as “declination” or “variation” in the world of aviation. Declination is different for different parts of the world. In Washington state, the declination angle is 20 ° east. This means that magnetic north is 20 ° east of true north. In Tennessee, the declination angle is 0 ° and in Maine, it is 20 ° west.
Declination values can be found in the margins or legend of topographic maps. Because the point of magnetic north is constantly moving, it is important to have a recent topographic map to find your way through the forest.
A similar point to remember is that compasses are calibrated for different parts of the world. So when shopping for a compass, make sure it’s designed to be used in the area of your big hiking vacation.
How to find your bearing
Follow these steps to find your bearing:
1. Position the compass on the map with the arrow on the motherboard pointing in the direction you want to go.
2. Rotate the compass dial so that the north of the compass is parallel to the north of the map.
3. Place the compass level in the palm of your hand and turn until the compass needle lines up with the north mark on the face dial.
4. The large arrow on the base plate is now aligned with its bearing.
Declination value and bearings: a trick to get it to stick
If you walked 10 miles through the forest in Washington state, regardless of the decline value on your bearings, you would end up more than 3 miles off target. That is too much!
To avoid confusion when looking for directions, keep the central principle in mind:
Make heading map = magnetic heading.
You will achieve this in the field by adjusting your bearings to compensate for magnetic declination. There are 2 ways to account for magnetic declination when finding your heading: an adjustable compass, and dialing your non-adjustable compass.
The simplest way is with an adjustable compass. Simply turn the compass declination adjustment screw to the correct value and all readings will automatically be converted to true north. If available, it is always best to have an adjustable compass when walking.
The next best way to account for declination is to mark the declination value on your non-adjustable compass at the beginning of your trip.
That is simple to do. For example, when the map indicates a declination value of 20 ° west, it will mark your compass dial at 340 °. If the map indicates a declination value of 10 ° east, it will mark your compass at 10 °. Make the mark with a permanent marker and then erase with isopropyl alcohol.
Now when you are facing the field, place the compass level in the palm of your hand and rotate it until the compass needle lines up with the declination mark on the front dial. Then the large arrow on the motherboard will point your bearing and automatically compensate for magnetic declination.