| To understand declination you must first realize that there are
two North Poles. There is a True Geographic North Pole at the top of the world, and a
Magnetic North Pole which is over 1,250 miles from the True North Pole. A magnetic compass
always points toward the Magnetic North Pole. Maps are oriented to the True North Pole.
The angular difference between True North Pole and Magnetic North is called declination.
Declination varies from 0 to 30 degrees in most populated regions of the world. These
declination values usually change slightly over time, as the earths plates shift. The
actual value of declination and its annual rate of change for your area will usually be
shown on your map. This will be expressed as either a Easterly or Westerly declination,
depending on your location. Below is an actual declination chart from 1990, showing the
worldwide declination situation in 1990. The current declination values for today will be
very close, if not identical, to the values below. 
The correction for declination is easily made. Once you
have aligned your compass on the map in your direction of travel, and rotated the capsule
to match the map's North-South directions, you are ready to make adjustments for
declination. (If you are not sure how to align your compass with your map, please see How to Use a Compass for more details). At this point, you
simply subtract Eastern declination from or add Western declination to this direction and
turn the capsule so that the new direction aligns with the index mark at the top of the
baseplate.
For example, using your map you have turned your capsule
to show 60 degrees at the index mark. Your local declination is 15 degrees Western. Your
corrected declination is then 75 degrees (= 60 degrees + 15 degrees). Reset your capsule
to 75 degrees.
Many compasses have a fixed declination correction scale
to simplify the calculations required. Some compasses even have an adjustable declination
correction scale that will allow for the declination compensation. With this type of
compass, the true direction can be used directly from the compass. Before buying a
compass, you may want to consider whether it has a fixed declination corrrection scale,
and adjustable declination correction scale, or neither.
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