66               Total Distance

 

Compass notes as per "Marin Outdoors"

COMPASS
The compass is a fairly simple piece of equipment that was invented by the Chinese around 2500 B.C. It consists of a magnetized piece of steel balanced on a pivot so that it is free to swing in any direction.

NEEDLE
The north end is usually painted red (occasionally black), stamped with the initial N, formed in the shape of an arrow, or a combination of the above. When left to itself it will eventually come to rest with one end pointing to magnetic north. To bring the needle to rest more quickly, it is suspended in a sealed compartment filled with air or liquid.

• AIR FILLED compasses work just fine, the drawback is that you must wait quite some time for the needle to come to rest so that you can take a bearing. It also requires that it be held stationary, so does not work well when hand held.
• LIQUID FILLED compasses are the most effective in breaking the swing of the needle quickly. The majority of compasses on the market are liquid filled with a mixture of water and alcohol.

ORIENTING ARROW AND LINES
The orienting arrow is the large arrow in the center of the compass pointing to North on the azimuth dial. Its double lines capped with a peak resemble a dog house, and it is frequently referred to as such. Orienting lines run parallel to the orienting arrow and help you to set the course. These, and other markings, are sometimes fluorescent, which provides better viewing at lower light levels such as early morning or evening, and in bad weather.

AZIMUTH RING (Bezel)
This is the dial surrounding the compass arrow that indicates degrees, from 0 to 360, in a full circle. Graduations, or degree markings, are listed by either 1, 2, 5 or 15 , with the more complete graduations providing greater accuracy. The 15 graduations are not recommended. To adjust for declination, the difference between magnetic north and true north, compasses feature a stationary, rotating, or adjustable azimuth dial.

• STATIONARY azimuth dials require that you turn the compass itself in order to align the arrow (magnetic north) and the "dog house" on the compass. You must manually correct your reading each time to reflect the declination.
• ROTATING azimuth dials allow you to adjust your compass setting for declination by aligning the arrow (magnetic north) and the "dog house", and then adjusting the dial by the degree difference of declination. This only needs to be done each time you start off on a new bearing.
• ADJUSTABLE, set screw, azimuth dials operate like the rotating ones, but the set screw allows you to rotate the orienting arrow to compensate for declination and then lock it into place. This only needs to be done once, at the start of your trip. This is a nice feature if you are going to be using it frequently in the same area.

BASE
The base plate is almost always clear, in orienteering compasses, so that you can see through it to the map for better alignment. The direction of travel arrow runs down the center of the base plate from the azimuth ring to the front, and is often marked "read bearing here".

Magnifying lenses are frequently inset into the base plate and are very helpful when looking at details on the map since the markings are quite small. Map scales are marked on the edges of the base like a ruler. Those with more than one scale will generally show 1:24,000 and 1:365,000 since these are the two most common.

Rounded corners are more comfortable in the hand, and some feel they slide more smoothly across a map and its folds. Levels are not necessary but improve accuracy, especially when hand held.

A lanyard, watchband, zipper pull, or tripod mount allows you to fasten the compass onto the outside of your body or pack, keeping the compass handy. They should not be made of metal.

SIGHTING DEVICES
These help you to more accurately take a line of sight heading to your chosen landmark. There are both mirror and lensatic sighting devices.

• MIRROR devices have a vertical line marked in the center of a hinged lid, with a notched sight at the top. First line up your chosen landmark in the notched sight at the top of the mirrored lid. Then align the center of the needle pivot with the vertical line in the mirror. You can now accurately read your bearing in the mirror. This device gives you approximately 2 degrees of error instead of the approximately 5 degrees of error that you get with a simple compass.
• LENSATIC devices have a vertical sight in the lid and a separate lens that is both used to align your landmark and read your bearing. As with the mirror device you sight your bearing, line up the vertical sight with the notch on the lens, and read the bearing. Because these are more accurate than the mirror devices, they are used by the military and often called marching compasses.

CENTER SPOTTERS
Similar to a telescope or binocular in appearance these provide no magnification. The compass and sight are inside. This allows you to sight a landmark and take your bearing all at once.

CLINOMETERS
These are used to measure the angle of incline. This angle, combined with a known distance, can be used to calculate height or, with a known height, distance. It is also used for determining slope and, in snow conditions, predict avalanche hazard.

SUGGESTED READING

• Be an Expert With Map and Compass
• U.S.G.S. Topographic Map Symbols (Free)

WHICH WAY?
There is an art to using the map and compass to discover where you are, determine where you want to be, and enable you to get there. Necessary, since there aren't many road signs or gas stations (for directions) in the wilderness.

ADJUSTING FOR DECLINATION
This is harder to understand on paper than it is in practice. You can either turn your map to adjust for the difference between true north and magnetic north, or add (or subtract) the difference to your original bearing. This is more important when orienteering, for sport, than when on a short hike.

ORIENT YOUR MAP

• Open the map on a flat surface.
• Set the compass dial so that north aligns with the bearing indicator mark on the compass base.
• Position the compass on the map with the long edge of the base plate aligned with the magnetic north arrow, labeled MN, printed in the map margin.
• While watching the compass dial, turn the map until the magnetic compass needle aligns with the "N" mark on the dial. Be sure no metallic objects influence the compass such as stoves, equipment, belt buckles, or jewelry (gold will not affect it, but other metals containing iron or steel will).
• Your map is now oriented, so you don't have to adjust your magnetic bearings when using the map and compass together.
• With your map oriented, you can pinpoint your position, determine your route, or find a campsite.

WHERE ARE YOU ON THE MAP?

TERRAIN ASSOCIATION is simply matching up the terrain features that you can see with those on your map, and thus locating your position.
TRIANGULATION involves sighting on two or more features. You take their bearing, find them on the map, and draw a straight line from the feature, going in the direction of that bearing. The point where these lines intersect is your position.

FINDING YOUR WAY

TAKING A FIELD BEARING is a visual means of navigating your route.

• Hold the compass level at waist height and point the direction of travel arrow at the feature that is your destination.
• Rotate the azimuth dial until the orienting arrow is centered with the red "N" end of the needle.
• The bearing can now be read in degrees at the center index line.

TAKING A MAP BEARING uses the map to plot and execute your route.

• After orienting your map, place the compass on the map with the baseplate edge connecting where you are and where you want to go.
• Set the compass heading by turning the dial until the "N" points to North on the map.
• Hold the compass level, in front of you; point the direction of travel arrow straight ahead.
• Turn your body until the red end of the needle is directly over the orienting arrow, pointing to the "N" on the dial.
• The direction of travel arrow now points precisely to your destination. Look up, sight on a landmark and walk to it.
• Repeat this procedure until you reach your destination.

OFFSET NAVIGATION
This is simply planning to arrive somewhat to the right or left of your target so that, for example, when you reach the trail you know which direction to take to arrive at your planned intersection.

BACKTRACKING
Reciprocal bearings and headings, sometimes marked on the azimuth dial, are simply the reverse of your original bearing, or 180 different. For example: For an original bearing of 20 NE, the reciprocal bearing is 200 SW (20 + 180). If math isn't for you, simply line the red arrow up with south instead of north and use the same heading you took to get there.