Navigating with a compass

One of the items in the 10 essentials is the compass. In the United States, most trails will be clearly marked. However, when you want to leave the trail and go "cross-country" or find a heading of an object on a map, nothing is better than a compass³.  A compass is a free floating magnetic device that point to the magnetic north pole on the Earth. We use this to help us navigate as it points us to a fixed point of reference.

I. Basic parts

Some compasses have more advance features built-in to it.  But each compass should have the following 2 basic components.

Component #1:The rotating frame contains the following:

On the circumference of the compass frame,  there is subdivision that is usually divided into 360⁰ or  400 grad, with markings around the frame.  Within this frame component there are these parts:

• 1a: Magnetic needle:

This needle is a free floating arrow lying horizontally within the frame. This needle has a red or luminous markings on one side of it and always points toward "magnetic north."  Depending on your location, the difference between "true north" and "magnetic north" is called the "declination."  This needle is used in combination with the orienting arrow to orient directions.

• 1b: Orienting Arrow: 

This arrow sits on the frame and does not throw off the magnetic arrow.  It moves with the frame as it is turned.  This arrow is used to orient the compass.

• 1c: Heading lines: 

Component #2: The fixed baseplate contains the following:^3,4  

The baseplate is where everything sits on. It does NOT move. It has the following parts:

•   2a: Direction of travel arrow (DTA): 

This arrow is etched on the head of the baseplate. It shows you which direction to travel when the compass is correctly oriented. 

•  2b: Inch & metric scale: 

This is used to measure the distance between points on the map.

• 2c: Index pointer

This pointer is used to read the bearing when the compass is dialed in and is correctly oriented. 

II. How to use the compass:

A. Finding true north:

In order to find "true north," we must know the error in the true north and the magnetic north in your area. This error is called the "magnetic declination" and is usually marked on the map.  Below is a magnetic declination map of the US. 

First, find the declination for your area. Then lay the compass flat and horizontal to the surface of the earth.  Rotate the frame so that the declination is pointing to the index pointer using the following formula (360⁰-x⁰E), (0⁰+x⁰W). Then turn the whole compass so that the red magnetic needle is aligned with the orienting arrow. The direction of the Arrow of Travel (DTA) is the "True North."

Examples:

(a) In the Orange County, California, USA, the average declination is 15⁰ to the E⁶. Turn the frame so that 345⁰ (360⁰-15⁰E) is on the index pointer.  Next rotate the whole compass so that the red magnetic arrow lines up with the orienting arrow. True North will be the direction of the DTA..

(b) In Washington D.C., USA the declination is 10⁰ to the West.³  Turn the frame so that 10⁰ (0⁰+10⁰W) is on the index pointer.. Next rotate the whole compass so that the red magnetic arrow lines up with the orienting arrow. True North will be the direction of the DTA..

Note: When using a compass, stay away from metal objects and power lines as it can affect the performance of the compass needle. Follow this distance chart.

B. Bearing: 

Example:

Heading is East, bearing is 90⁰;
Heading is West, bearing is 270⁰ (no such thing as a bearing of -90⁰ or`90⁰W).

C. Three scenarios to follow a compass heading:

We have a bearing of 124⁰.

• Lay the compass horizontal and dial the frame to 124⁰ on the index pointer.
• Rotate the whole compass so that the magnetic needle is aligned with the orienting arrow.
• The direction of the DTA will have a bearing of 124⁰.

• Lay the compass horizontal at eye level.
• Point the DTA toward the object you want to find the bearing for.
• Rotate the frame so that the red magnetic needle lines up with the orienting arrow. (See picture (a) & (b).
• Bring down the compass and read the bearing on the index pointer.
  

3.  Find a bearing of an object on a map: (See Navigating with a Map)

 IV: Various Compass