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Conditions:
Given a standard 1:50,00-scale military map
with a declination diagram, a pencil, and a
magnetic azimuth and a grid azimuth that
must be converted.
Standards:
Converted the given magnetic azimuth to a
grid azimuth and the given grid azimuth to a
magnetic azimuth without error.
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Performance Steps
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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).
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Figure C-30.
Declination diagram
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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).
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Figure C-31. G-M angle |
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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.
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4.
The G-M angle depends on where
you are in the world.
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5.
Convert azimuths when given an
easterly G-M angle (figure C-32).
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Figure C-32.
Converting azimuths with easterly G-M
angle
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a.
To convert a magnetic azimuth
to a grid azimuth, add the value of
the G-M angle to the magnetic azimuth.
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b.
To convert a grid azimuth to a
magnetic azimuth, subtract the G-M
angle from the grid azimuth.
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6.
Convert azimuths when given a
westerly G-M angle (figure C-33).
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Figure C-33.
Converting azimuths with westerly G-M
angle
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a.
To convert a magnetic azimuth
to a grid azimuth, subtract the value
of the G-M angle from the magnetic
azimuths.
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b.
To convert a grid azimuth to a
magnetic azimuth, add the value of the
G-M angle to the grid azimuth.
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Evaluation
Preparation:
Setup:
Give the soldier a standard 1:50,000-scale
military map, a piece of paper, a pencil,
and a magnetic and grid azimuth to be
converted.
Brief
Soldier: Tell the soldier to convert the
magnetic azimuth to a grid azimuth and the
grid azimuth to a magnetic azimuth.
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Performance Measures
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GO
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NO
GO
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1.
Determined correct grid
azimuth.
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——
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——
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2.
Determined correct magnetic
azimuth.
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——
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Evaluation
Guidance:
Score the soldier GO if all
performance measures are passed. Score the
soldier NO GO if any performance measure is
failed. If the soldier scores NO GO, show
what was done wrong and how to do it
correctly.
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References
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Required
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Related
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FM
3-25.26
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FREE Audio Version
Download & print
Misc. Information
For
55 years, this has been the basic guidebook for enlisted leaders
of the Army.
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