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Land Nav Task 10 - Orient a Map Using a Lensatic Compass

Standards: Oriented the map to the ground using a compass so the north-seeking arrow of the compass was within 3 degrees (20 mils) of the angle shown in the grid-magnetic (G-M) angle of the declination diagram shown on the map.

Conditions:
Given a field table, a standard
1:50,000-scale military map, a protector, a
pencil, paper, and a compass in daylight.

Standards:
Oriented the map to the ground using a
compass so the north-seeking arrow of the
compass was within 3 degrees (20 mils) of
the angle shown in the grid-magnetic (G-M)
angle of the declination diagram shown on
the map.

 

Performance Steps

1.  
With the map level, place the
compass parallel to a north-south grid
line with the cover side of the
compass pointing towards the top of
the map. This will place the black
index line on the dial of the compass
parallel to grid north. Because the
needle on the compass points to
magnetic north, a declination diagram
on the face of the compass is formed
by the index line and the compass
needle.

2.  
Rotate map and compass until
the directions of the declination
diagram formed by the black index line
and the compass needle match the
direction shown the declination
diagram printed on the margin of the
map. The map is then oriented.

3.  
If the magnetic north arrow on
the map is to the left of the grid
north, the compass reading will equal
the G-M angle (given the declination
diagram). If the magnetic north is the
right of the grid north, the compass
reading will equal 360 degrees (6400
mils) minus the G-M angle.

4.  
Remember to point the compass
north arrow in the same direction as
the magnetic north arrow (step 2
above), and the compass reading (equal
to the G-M angle or the 360 degrees
(6400 mils) minus G-M angle) will be
quite apparent.

Note. If the G-M angle is less then 3 degrees (50 mils), do
not line up the north arrow.

5.  
Some maps have a built-in
protractor considering of a pivot
point "P" on the south neat
line of the map and several degrees of
arc along the north neat line of the
map. The G-M line is obtained by
connecting pivot "P" with
the appropriate value of the G-M angle
(taken from the declination diagram)
on the arc. The map may then be
oriented by placing the compass
parallel on this line and rotating the
map and compass until the needle point
is aligned with the continuous line
formed by the index line and the
sighting wire. The map is then
oriented.

6.  
An alternate method is to draw
a magnetic north line on the map from
any N-S and E-W grid line intersection
using the protractor. Align the
straightedge of the compass along this
magnetic north line and rotate the map
and compass together until the north
arrow falls beneath the fixed black
index line on the compass.

Evaluation
Preparation: 

Setup:
Select an area that is free of magnetic
interference (parlance, vehicles). Provide a
field table, 1:50,000-scale military map, a
protractor, a pencil, paper, and a compass.

Brief
Soldier: Tell the soldier to orient the
map to the ground using the compass. Tell
the soldier he must use the G-M angle shown
by the declination diagram if it exceeds 3
degrees (50 mils).

Performance Measures

GO

NO GO

1.  
Determined whether G-M angle
exceeds 3 degrees (50 mils)

2.  
Aligned the side of the compass
with one of the north-south grid
lines.

3.  
Positioned the cover of the
compass toward the top of the map.

4.  
Oriented the map.

5.  
Corrected the orientations of
the map when the G-M angle exceeded 3
degrees (50 mils) using one of the
following:

a.
Used the G-M angle formed by
the compass’ black index line and the
compass needle.

 

 

b.
Used the pivot point
"P" on the south neat line
and the degrees of arc along the north
neat line and placed the compass along
this line.

 

 

c. 
Drew a magnetic north line from
any N-S and E-W grid the intersection
using a protractor and placed the
compass along this line.

 

 

Note.
Step 5 is required only when G-M angle
exceeds 3 degrees or 50 mils. Step 5b
is tested only if the map has the
built-in protractor
.

 

 

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.

References


 

Required


Related


 

FM
3-25.26

 

 


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