10
M
agnetic declination is the angle between True North and Magnetic North. The
amount of declination at any given point depends on the location of that point on
the continent. Where True and Magnetic North are in the same direction, the dec-
lination is zero. In North America a line of zero declination runs roughly from west
of Hudson Bay down along Lake Michigan to the Gulf Coast in western Florida.
At any point west of that line, your compass needle will point east of True North.
This is called “Easterly Declination.” At any point east of that zero line, your com-
pass needle will point west of True North. This is called “Westerly Declination.” In
North America, magnetic declination varies from 30º east in Alaska to 30º west in
Labrador. See diagram on page 9.
Allow for Declination
W
here accuracy is not critical, ignore magnetic declination, especially in areas where
the declination is minor. You may also ignore it when the compass is used without
reference to maps and is based on field bearings only.
W
hen the compass is used with a map or in connection with map bearings, adjust-
ment should be made. There are two methods to accomplish this:
1. Temporary Method. You must redo every time you wish to apply it.
Find the amount of declination in their area and whether it is easterly or westerly.
This information is on topographic maps of the area.
Take your bearing from the map as described in Sect. D. and observe the degree
reading at the index pointer.
