Magnetic declination often confuses land navigators. As proof of this fact, manufacturers even make compasses you can set to automatically take care of declination issues.
But if you're wandering the back country, you are, in my opinion, a lot better off understanding the whole declination thing instead of just relying on some compass trick to take care of it for you. Mindless reliance on any thing mechanical is not a good idea if you really want to find your way.
In this 14-minute video, my goal is to present in a simple manner how to work with declination.
What is declination?
In order to mess with the mental tranquility of navigators, compasses don't actually point to true north, but to magnetic north. Strictly speaking, compasses don't "point" at all. They merely align themselves with the earth's magnetic field.
In only a very few places on earth, does this field cause a compass to align itself with true north. In most other places, the compass is aligned in such a way that its needle or dial points either somewhere to the west of north, or somewhere to the east of north.
When the compass points to the west of north, that's called west declination, and when the compass points to the east of north, that's called east declination.
When the declination is larger than 4 or 5 degrees, not accounting for it, can cause you problems in finding your way from point A to point B.
To help simplify things, my suggestion is you learn to deal first with the declination in your area, be it east or west. Once you're thoroughly familiar with how account for that, then deal with the opposite declination by doing just the opposite of what you normally do.
To deal with west declination, do the following:
When converting from a map, or true, bearing to a magnetic bearing, add the declination. When converting from a magnetic bearing back to a map bearing, subtract the declination.
Map to Magnetic +
Magnetic to Map -
To deal with east declination, do the following:
When converting from a map, or true, bearing to a magnetic bearing, subtract the declination. When converting from a magnetic bearing back to a map bearing, add the declination.
Map to Magnetic -
Magnetic to Map +