The document provides a history of the compass and describes how modern compasses work by using a magnetic needle or capsule to align with the earth's magnetic field. It explains the basic features of compasses like the measurement ring to observe angles and sighting mechanisms, and discusses common types of compasses and their uses for wilderness navigation like orientation, taking bearings, and plotting routes on a map.

1. The Compass

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.

6. Other Features Abound
• Distance Scales
• Magnifying Lens
• Slope Measurement
• etc…

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.

8. A Look at Some Common
Compass Types

9. Zipper Pull Compass
• Good for general
direction

10. Lensatic
• 5° markings
• So-so for sighting
• Useless for plotting

11. Baseplate
• 2° markings
• Good for map plotting
• Hard to sight on
a distant object

12. Mirrored
• 2° markings
• Good for sighting
• Good for plotting
• May have
adjustable declination

13. Sighting Baseplate
• 1° markings
• Best for sighting
• Good for plotting
• No declination
adjustment
• My personal favorite!

15. Parts of a compass

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.

17. Needle Parallax
View from Above View from Behind

18. Parallax Side View

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