Land Nav Task 9 - Convert Azimuths

1.  
The north-south lines on your
map give grid north. The needle of
your compass points to magnetic north.
Grid north and magnetic north are
usually different by a few degrees.
Neither one points straight to the
North Pole (called true north), but
you do not need to know true north to
keep from getting lost in a combat
area. The difference in degrees for
every map is shown on the bottom of
mapsheet (figure C-30).

Figure C-30.
Declination diagram

2.  
The difference between grid
north and magnetic north is called the
grid-magnetic (G-M) angle. The diagram
at the bottom of the map tells you how
to change grid azimuths to magnetic
azimuths and magnetic azimuths to grid
azimuths (figure C-31).

Figure C-31. G-M angle

3.  
For example, you aim your
compass at a distant point. The
compass reading you get is 190
degrees, the magnetic azimuth. The
diagram on your map (see figure 2)
tells you that the G-M angle is 9
degrees, and it also tell you that
"to convert a magnetic azimuth to
a grid azimuth, add the G-M
angle." Therefore add 9 degrees
to your compass reading. This gives
you 190 + 9 = 199. Your grid azimuth
is 199 degrees.

4.  
The G-M angle depends on where
you are in the world.

5.  
Convert azimuths when given an
easterly G-M angle (figure C-32).

Figure C-32.
Converting azimuths with easterly G-M
angle

a.
To convert a magnetic azimuth
to a grid azimuth, add the value of
the G-M angle to the magnetic azimuth.

b.
To convert a grid azimuth to a
magnetic azimuth, subtract the G-M
angle from the grid azimuth.

6.  
Convert azimuths when given a
westerly G-M angle (figure C-33).

Figure C-33.
Converting azimuths with westerly G-M
angle

a.
To convert a magnetic azimuth
to a grid azimuth, subtract the value
of the G-M angle from the magnetic
azimuths.

b.
To convert a grid azimuth to a
magnetic azimuth, add the value of the
G-M angle to the grid azimuth.