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. The Magnetic North Pole is always moving. It has been as much as 1,200+ miles from true north, but in 2005 is only around 500 miles from the True North Pole.
We typically say that a compass points to Magnetic North, not True North. Technically, that is not exactly true. The compass actually points in the directions of the horizontal component of the magnetic field where the compass is located, and not to any single point. Knowing the difference (measured in angular degrees) between true north and the horizontal trace of the magnetic field for your location allows you to correct your compass for the magnetic field in your area. This angular difference is called your 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 an 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. For current and more accurate declination values, visit our "Find your declination value"
page. Once you have your correct declination value, you should check out our How To Use Your Declination Value
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. Check here to see all our compasses with adjustable declination.
Before buying a compass, you may want to consider whether
it has a fixed declination corrrection scale, and adjustable declination
correction scale, or neither.
For more information on using a map and compass you may want to consider
purchasing this 144 page instructional compass book, Discover
A special thanks to Suunto for providing
the content for this useful page.