Using a Compass

1
Using a Compass

• What is a compass?
• How does a compass work?
• What are the parts of a compass?
• Using a compass.

2
What is a compass?

• A compass is a magnetized needle
• When allowed to move freely, points in the
  direction of Magnetic North.

3
Compass Directions

• This needle gives you a reference point for
  measuring all other directions.
• North top of needle
• South bottom of the needle
• East right of the needle
• West left of the needle

4
Compass Directions

• Half the distance between North and East is
  Northeast.
• Half the distance between South and West is
  Southwest.

5
Compass Directions

1. North
2. Northeast
3. East
4. Southeast
5. South
6. Southwest
7. West
8. Northwest

6
Compass Directions

• Splitting the directions again gives the compass
  user sixteen distinct directions.

7
How does a Compass work?

• A compass works with the earths magnetic field
  to find North.

8
How does a Compass work?

• Every magnet has at least one north pole and one
  south pole. 
• Unlike poles attract (Top).
• Like poles repel (Bottom).

9
How does a Compass work?

• In magnets, opposite poles attract each other.

10
How does a Compass work?

• Think of the Earth as having a gigantic bar
  (actually molten core) magnet buried inside.
• In order for the north end of the compass to
  point toward the North Pole, you have to assume
  that the buried bar magnet has its south end at
  the North Pole.

11
How does a Compass work?

• The "opposites attract" rule of magnets would
  cause the north end of the compass needle to
  point toward the south end of the buried bar
  magnet.
• The magnetic field created by the molten core of
  the earth attracts the "N" end of our bar magnet
  and compass needles. 

12
What is Magnetic North?

• The ends or poles of the magnet do not match the
  Earths geographic poles.
• The bar magnet does not run exactly along the
  Earth's rotational axis.
• It is skewed slightly off center.
• This skew is called declination.

13
What is Magnetic North?

• A compass points to magnetic north known as the
  Magnetic North Pole.
• The magnetic pole tends to drift, so its location
  can change over time.
• The drift is minor.

14
Does a compass work if you are standing at the
North Pole?
15
Can you use a compass near the North Pole?

• A compass becomes erratic as you approach the
  Magnetic North Pole and the true North Pole and
  becomes unusable.
• Yellow zone compass erratic
• Red Zone compass unusable

16
Types of Compasses

• Compasses are marked in several very different
  ways
• The Quadrant Compass
• The Military Compass
• The Azimuth Compass

17
Types of Compasses

• The Quadrant Compass
• Have a scale divided into four segments of 90
  each
• Used primarily by surveyors for establishing base
  lines and datum lines.

18
Types of Compasses

• Military Compass
• Is read in mils.
• Marked from 0 to 6400

19
Types of Compasses

• Azimuth Compass
• The dial on an azimuth compass is marked in
  degrees proceeding clockwise from the north.
• North is 0 or 360
• East is 90
• South is 180
• West is 270

20
Types of Compasses

• Azimuth Compass
• The azimuth compass is best suited for outdoor
  activities.
• Marked from 0 to 360

21
Parts of a Compass

• A compass has three main parts.
• Base (base plate)
• Housing
• Lid (cover)

22
Parts of a Compass

• Base
• On most compasses this is a rectangle made of
  plastic.
• It will have scales on both sides.
• The scales will have inches on one side and
  centimeters on the other. These are used with a
  map scale to determine the distance between two
  points.

23
Parts of a Compass

• Housing contains
• The needle (usually in a liquid filled container)
• The dial (azimuth dial) that can be turned to set
  or determine directions and is marked from 0 to
  360 degrees

24
Parts of a Compass

• The Cover or Lid
• Mirror on the inside with a direction of travel
  line down the middle.
• A sight to aim the compass is located on top of
  the lid.

25
Parts of a Compass The Housing

• Housing - This is the dial that can be turned to
  determine and set bearings or directions.
• Bearing/Sighting Line - Like the sights on a gun,
  this line is used to point the compass directly
  at a target.
• Needle - The needle is a thin strip of magnetic
  iron on a frictionless pivot. The red tip will
  always point toward the magnetic north pole in
  the northern hemisphere.
• Orienting Needle - The orienting needle is an
  arrow outline painted below the needle. It is
  part of the housing, and rotates with the
  housing. The top or front of the orienting needle
  is aligned with the north end of the needle when
  navigating.
• Grid Lines - Grid lines are used to align north
  on a map.

26
Parts of a Compass

• 1. Sight
• 2. Direction of Travel Line
• 3. Needle
• 4. Orienting needle
• 5. Housing (dial)
• 6. Grid Lines
• 7. Sight
• 8. Scales

27
Using a Compass

• A compass needle is sensitive to metal and
  magnets and can be affected by
• Metal belt buckles, rings, and watches
• Metal fences
• Metal buildings
• Automobiles
• Gun barrel
• Electronic accessories
• Be aware of similar objects to eliminate false
  readings

28
Using a Compass

• To use the compass , you need to
• Hold it steady and keep it away from metal.
• Place the compass in the palm of one hand and
  place that hand in the palm of your other hand.
• Pull your elbows firmly into your side.
• Hold the compass steady and level, this allows
  the needle to move freely.

29
Using a Compass

• While holding the compass level, point the
  direction-of-travel arrow (or sight) in the
  direction you want to travel.

30
Using a Compass

• Then turn the compass housing until the compass
  needle aligns with the arrow marks drawn on the
  bottom of the compass. Remember, the colored end
  of the compass needle points north.
• Now move so that you are looking straight ahead
  in the direction in which you want to travel. Be
  sure that the magnetic needle still points north.
  
• To keep from straying too far to the left or
  right of direction-of-travel, pick an object as
  far away as possible to align yourself.
• Stop occasionally to make sure you are headed in
  the correct direction. Keep repeating this
  process to stay on course.