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Basic Use of the Magnetic Compass
What is a Compass
• The current, hand-held magnetic compass is two
• A north-seeking device from which you can determine
direction of travel, and (with the aid of built-in scales)
the relative locations of items within view. Some of
the features on the compass have nothing to do with
• An instrument to help you plot onto maps your
position from observations, and to plan routes. Some
of the features on the compass have nothing to do
with this function.
• Bearing is the direction to a target item or destination.
Azimuth has essentially the same meaning.
• Heading is the direction you are travelling (the way you
• Magnetic North or MN points towards the magnetic north
• True North, sometimes TN or denoted with a star points
towards the geographic north pole at the center of the
• Grid North or GN is the direction in which the north/south
grid points at the center of the map sheet.
• The capsule is the container where the needle floats. A
graduation ring around the edge of the capsule denotes
• Declination is the deviation
between magnetic north (where
the needle points) and true north.
• To navigate based on information
plotted from a map or similar
system, you have to account for
• Declination varies greatly by
• Declination is listed on maps, but
changes over time so be careful
with older maps.
Degrees, Mils & More
• Degrees are as usual, 360° make up a circle.
• Mils is short for milliradians. 6400 make up a circle*.
These are common in artillery, machinegunnery and
generally on military compasses.
• Cardinal points (“NNW,” etc.) and even colors can
also be used to denote direction.
Any system will work fine as long as you are the only
one using it. If you work with others, you have to use
the same system as them to be able to communicate.
* A mil is not a mil. The US (and now NATO) standard is 6400, but older Swedish compasses use 6300 mils in a circle, older UK compasses,
6280, and the Russians 6000. Be careful if using surplus, foreign or captured equipment in a shared working environment.
If you are wondering, a radian is mathematically (geometrically) interesting. Its the angle in which the radius is equal to the curved length of
the arc. A “real” milliradian puts 6283 milliradians in a circle.
Baseplate Compass: Sighting
This applies to any baseplate (usually, clear baseplate), protractor or Silva 1-
2-3 style compass.
1. Hold the compass level, in front of you, so you can see sort of across
and down into the capsule. You will need to see the needle and the
north mark on the graduation ring.
2. Turn yourself until the red end of
the needle points exactly north
(360°, 0, etc.) on the graduation
ring. Most clear basepate
compasses also have a red arrow
in the bottom of the capsule you t
can use for this alignment.
3. To use this in conjunction with a
map, read the bearing to the
target off the top of the
Baseplate Compass: Plotting
1. Place compass on your map with the
edge along your desired line of travel.
2. Rotate the capsule until North on the
graduation ring point towards North on
the map (you may need to draw
additional faint pencil line on the map
more frequently than they are printed).
The capsule base will have lines in it to
help with this.
3. The compass is now set up for
navigating to a destination.
4. A compass already sighted on a target
can be used in a reverse procedure to
determine (or confirm) your location on
Baseplate Compass: Travelling
1. If you are travelling to a location you
just sighted, the compass is already
setup correctly. Otherwise, you will
have set the compass up during the
2. Keep the needle pointing towards north to know the bearing to your
destination. The compass can be referred to by holding it against
your chest (center hold method). The compass body will then be
pointing the way you are; just glance down to see which way you
3. Line up the needle and north mark, as when sighting, to find a
reasonably nearby feature on your path like a tree or distinctive hill.
Walk to there (as convenient), then take a bearing to another point
and walk there. Repeat until you reach your destination.
Differences in the Ranger
The Silva Ranger series is the definitive mirror-sighting style of compass.
Perform most functions as for a conventional baseplate compass.
To sight a distant object:
1. Hold the compass with the capsule at eye
level. The mirror will be up at about 45°, so
you can clearly see the reflection of the
capsule and the needle.
2. Use the line on the mirror (and any notches
on the cover) to precisely align the compass
and yourself with the target.
3. Without moving, twist the capsule so the
direction-of-travel arrow aligns with the north
end of the needle.
4. Read the compass, or just use this
alignment to walk this bearing.
Lensatic Compass: Sighting
● The US lensatic compass can be
quickly sighted over the top in the same
manner as a baseplate compass.
● For more precision, place your thumb a
thru the loop, fold the lens forward and
the cover somewhat rear, and hold the
assembly against your cheek, as in the
● Use the notch above the lens with the wire in the lid to sight on a
target. Lock the bearing by folding the sight forward.
● You may then read the bearing directly, or lock it in for further
navigationby twisting a bezel on top of the capsule. A tritium line
on the glass is aligned with the north needle.
Lensatic Compass: Plotting
• The compass is not used for
plotting on the map; a clear card
device called a roamer or
protractor is used instead.
• To avoid drawing lines on maps,
or carrying another straightedge,
attach a thin string to the center
of the protractor.
• The line can be drawn from the center to the target to determine
angles, which are read off the edge of the card. Both degrees and
mils are included.
• Small triangle within the card provide additional precision within
grid squares for various map scales.
Lensatic Compass: Travelling
• When travelling, its best to use the lensatic much like the
baseplate compass; hold the compass against your chest,
so you can glance down and see the capsule and
• If the needle and the luminescent indicator is aligned, you
are on course.
• If your waypoints are very far apart, and there is time to
stop, it may be valuable to use the lens/lid sighting method
to more precisely pick the best target.