2. Some History
• As far back as 2500 BCE the Chinese knew
that a loadstone on a piece of floating wood,
would always point itself in the same
direction.
• Later with the move from bone to iron
needles, it was noticed that an iron needle
placed near a loadstone would also take on
these directional properties.
3. The Modern Compass
• Modern compasses typically have a
magnetic needle or capsule that floats freely
on a central pivot, so that it can align itself
with the earth’s magnetic field.
• Electronic compasses, with no moving
parts, are made by measuring small currents
in coils of wire, induced by the earth’s
magnetic field.
4. Angular Measurement
• A compass will have a angular measurement ring to
observe the angle between the compass needle and the
compass body.
• The most common angular measurement system is a 360°
circle.
• Other systems include
– Four 90° quadrants
– Mills, a system that divides a circle into 6400 parts
– Avoid these for wilderness navigation purposes
5. Sighting Mechanism
• Many compasses include some mechanism
for sighting to a distant point to measure the
angle of the line to that object relative to the
compass needle.
7. Compass Uses
• In wilderness navigation a compass is used
to do the following.
– General orientation to the 4 cardinal directions
– Taking a bearing to a distant object
– Traveling along a heading
– Plotting or measuring a bearing on a map
• This is using the compass as an expensive
protractor, and does not use it’s magnetic direction
capabilities.
16. Taking a bearing to an object
• Sight to the object with the compass.
• Turn the ring to align the orienting arrow
with the red end of the magnetic needle.
• Read the bearing from the ring
at the index line.
19. Needle Parallax
Good Bad
Keep the needle parallel to the meridian lines.
20. Taking a back bearing
• A back bearing is taken looking back to
where you took the original bearing.
• A back bearing is 180° different from a
forward bearing.
• An easy technique is to align the south end
of the needle rather than the north end.
21. Classroom compass exercise
• Pair up with another student
• Take a bearing and a back bearing on each other.
• Bearings should agree within +/- 2°
• Try other positions in the classroom
• Try using other types of compasses
