WHAT IS A GOOD BASIC ORIENTEERING COMPASS.
It will have a Steel Magnetic Needle painted Red for North, that glows in the dark.
It will have a Sapphire Needle Bearing that eliminates errors caused by friction of the pivot.
It should have a sealed, liquid filled, needle housing, to dampen the swing of the needle in under 4 seconds.
It will have an easy to grip rotating Graduated Dial, marked in at least 5 degree or 2 degree increments, from 0 to 360 degrees.
It should have a see-through Base Plate with a DIRECTION OF TRAVEL ARROW on it for sighting along bearings.
It will have an ORIENTING ARROW under the needle for orienting to declination.
It should have ORIENTING MERIDIAN LINES under the Compass Needle, for orienting to True North or Magnetic North "Meridian Lines" on the Map.
A ruled straight edge on the flat BASE PLATE to convert inches into miles on a standard Topo Map, Millimeter, and Inch scales.
Lanyard for carrying around on neck.
Other conveniences include...
A Sighting Mirror, with a Sighting Line, for viewing both the distant landmark, and the Compass Rose bearing numbers. It is used to get a very accurate reading. (Is also good for shaving and signal aircraft rescuers.)
Built in magnifying lens to see tiny Map names, and altitudes.
Inclinometer or Clinometer to measure the steepness of trails, to shoot angles to distant peaks and help locate your position.
The more expensive Compasses, have an Adjustable Declination Set Screw. This moves the Orienteering Arrow inside the Needle Housing. Once set, it takes care of all mathematic conversions for declination, between Field Bearings and Map Bearings, automatically. (This is the same as placing a narrow piece of tape on the Compass housing to be discussed later. This IS the "True North Method.")
Some have an Adjustable Needle Housing that twists and can be reset within the Compass Rose to compensate for declination (Braun).
Every one in the wilderness should have a Map & Compass and know exactly how to use it.
The magnetic field of the Van Allen Belt, which surrounds the Earth, is not easy to understand. For one thing it does not run directly through the Earth's center of gravity. It is off- set by several thousand miles away from the center of spin as it runs under the pacific ocean to the southern hemisphere. This causes a different amount of "dip" to be measured along the same latitude through out the world.
For another thing, the Equator, is the only place on the planet where the magnetic lines of force are completely parallel to the ground. Every where else on the planet, the magnetic field points down into the Earth at an increasingly steep angle as we move towards the poles. This vertical angle component, between the magnetic lines of force, and the flat ground, is called "Magnetic Inclination" or "Dip."
At latitudes greater than 65 degrees North, the horizontal magnetic component of the Earth's field, needed to deflect a compass, becomes too weak and erratic for finding directions. Shipboard navigators are required to use non-magnetic gyro compasses (spinning at 26,000 revolutions per minute), Lorans, Omegas, or Celestial Navigation (star charts & Sextant) to triangulate their positions.
(A Loran is a radio that picks up transmitted timing signals. It measures the intervals between 2 incoming signals, and shows the distance to the beacon stations. Omegas use frequency phase shift much the same way as Loran uses time delay, for locating a ships position along well defined shipping lanes.)
The increasing strength, of the vertical magnetic lines of force, as they converge into the ground at the poles, are many times stronger than they are at any other place on the planet.
Compasses are manufactured with the proper amount of counter weighting, and the proper amount of magnetizing lines permeating the needle. They are made in close proximity to the actual angles of force it will encounter in a specific continental location in the world.
As an example, as a "made for U.S." compass, nears the pole region, the magnetic needle will increasingly begin to point into the earth. You'll have to hold the compass housing unevenly to get any kind of reading at all. All the needle wants to do is point into the ground, and not to the horizon. Maybe a Needle with a weaker magnetic field, or counter weighted differently may help. However there are places on the globe where it is impossible to get any reading at all, with any kind of magnetic compass, due to this phenomenon of "dip."
So if you are going to Alaska, Finland, or Australia, be sure to pick up a Compass made for that area, as your made for U.S. Compass will prove to be unreliable.
And finally, still one other problem with the Earth's magnetic field. One with which we will have to deal with more directly.
Only at 2 North/South lines in the northern hemisphere, does the compass needle point to True North. One is through Russia and the other is Wisconsin & Alabama in the U.S.. At all other places on the globe, the Compass will either point East, or West, of the actual Geographical True North, by an angle called "Magnetic Variation" or "Declination." This is the name given to the angle, between True North, and Magnetic North. Magnetic North is located about 1,000 miles South of Geographic North, near Bathurst Island, centered off the Northern coast of Canada above Hudson Bay.
In the continental United States, this angle of error is going to be between 25 Degs East, to about 23 Degs West of True North. Alaska's declination ranges from 15 Degs East to 36 Degs East.
And to top it all off, these values will slowly change over time, as the earth's continental drift moves the crust over its molten mantle at 2 to 4 inches per year. Along with that, on June 27th, 1992, the San Bernardino Big Bear 6.2 earthquake caused the San Bernardino Mountains to jump over the valley by 1.5 feet in places. This in turn twisted the valley floor slightly, and caused the declination of the valley to actually gain 1/2 degree in 30 seconds, from 14.75 Degs to 15.25 degrees.
To find a declination for an area you would wish to visit, you can always call an airport's Flight Control Center, 24 hours a day, to get a very accurate Declination. Even the best Topo Maps can be slightly off.
So what I need you to under stand is when using a Compass, you have to always compensate for declination one way or another. You can either draw "Magnetic Lines" on your maps, or let the compass correct for Declination for you.
A compass can give an incorrect reading if it is in the presents of iron, steel, or the presents of electrical wires that makes a local magnetic field. These will prevent the Compass needle from correctly pointing to Magnetic North, and can help throw you way off course. When finding North, watch out for nails in picnic tables, Belt buckles, Knives, Lighters, Karabiners, and even red rocks (which happen to contain iron), that you may set your compass on. And forget even trying to use the compass to orient a Map on the hood of your car.
Bearing is a horizontal angle, that fixes a direction in respect to True North, (or Magnetic North), as measured in a clockwise direction on the Compass Rose.
Some Compasses use a different system of direction expression, than Azimuth, found on your regular Camping compasses.
One of these other types is called the QUADRANT SCALE Compass. The graduated dial is still marked off with 360 degrees all the way around, but it is very different from the normal Azimuth Scale you may be used to.
The Quadrant Scale system calls North - 0 degrees, and increases to 90 degrees at West, then decreases again to 0 degrees at South, and then increases to 90 degrees at East, and 0 degrees at North again.
Direction Azimuth Quad North 0/360 0/0 East 90 90 South 180 0 West 270 90
Directions are given in quadrants such as "North 20 degrees East" (Equals an Azimuth of 20 degrees), or "North 15 degrees West" (Azimuth of 345 degrees), or "South 40 degrees East" (Azimuth of 140 degrees) or "South 10 degrees West" (Azimuth of 190 degrees). This system is based on Polar Rectangular Coordinates, for use by Foresters, Surveyors, Geologists, Builders and Engineers.
Another system, the METRIC SYSTEM, has its own version of the Azimuth Dial also, and it Breaks the regular 360 degree dial, into 400 Grads. This means that 90 degrees East, is also equal to 100 Grads East, and South is 200 Grads. This is further broken down into Centigrads (1/100th of a Grad), and Milligrads (1/1,000th of a Grad). These are extremely fine angular measurements, and much finer than you need to bother about in the field.
Another system is the military usage of the MIL. The regular 360 Azimuth degree circle, equals 1,600 mils. So East is represented by 400 mils, South is 800 mils. It is used mainly for aiming military Gunnery.
We have already talked about "clicks." It is a forward tactical military direction expression. 90 Degrees East Azimuth equals 30 clicks, and 180 Degrees Azimuth equals 60 clicks.
It is unlikely that you will need to know these other Azimuth Markings, but they do exist, and show up occasionally.
The type of graduated dial used by most Outdoorsman is the AZIMUTH SCALE. A system of 360 degrees.
Just to make you aware, there are a few types of "bearings," and is important that you know the difference between them. Look at your map's Declination Chart. There are True Bearings (measured from True North), Grid Bearings (measured from Grid North), and Magnetic Bearings (measured from Magnetic North). These expressions are referring to the "Degree of Angle" between a "Direction of Travel," and the angle of either Grid North, Magnetic North, or True North. So any Direction can be expressed as 3 different bearings, and still be correct. It becomes important that all bearings be defined as 260GN, 50TN, or 180MN.
In addition, there are Map Bearings, and Field Bearings.
A Map Bearing, is a bearing taken while looking at a Map, to be applied to the land, and can be expressed as Grid, Magnetic, or True North.
A Field Bearing is taken while looking at the landscape, to be applied to a map, and can also be expressed as Grid, Magnetic, or True North.
In this Syllabus you will be taught "True Bearings" in relation to "True North" only, mostly because maps are True North.
First the bad news... Using a Compass to locate North in the field (Field Bearing), is different than finding North with a Map (Map Bearing). This is due to the Magnetic Declination. The Map (True North), and the magnetic needle (Magnetic North), speak 2 different languages.
Whatever distance you travel, for each degree of declination you don't account for, you will be off your course 1/60 of the total distance traveled.
This means that at 15 degrees declination, at 1 mile out, you can be 1/4 of a mile off course. Just imagine how important Declination would be in Alaska at 36 degrees...
To correct for these differences, mathematic conversions are necessary. We need to "add" or "subtract" our local Declination, to our bearing, every time the Compass is used...
In the western United States, for Map Bearings, to convert to Field Bearings, add your local declination to get the correct Magnetic Bearings to be applied to the land. For Field Bearings, subtract your local declination to apply to the map. On the east coast, the opposite math needs to be preformed. Let's face it, in the real world of the wilderness, it is NOT EASY to remember when to add and when to subtract.
Now the good news... There is however, a couple of ways to completely eliminate the mathematical differences between Magnetic North and True North, so you never have to think about them again.
The "Magnetic North method" uses a series of parallel lines that YOU draw on the Topo Map, parallel to the Declination Chart at the bottom of the Map. These new drawn Map lines then represent your new "Magnetic Meridian lines" pointing to Magnetic North, so that the Compass needle, Compass Housing, and the Map, all speak the same language. From this time forward, the Compass is used "Magnetic Needle" to "Magnetic North on Housing" to "Map Magnetic North" to get a Bearing, and we can completely forget declination. All bearings are then given as degrees from Magnetic North to your Bearing or heading. Be sure to mark it MN when you write it down.
"Boxing the Compass," is the oldest way on the planet to orient a Map using a simple Fixed Dial Compass, having no Magnetic Meridian lines drawn on the Map. The map is placed on the ground, and the Compass is placed on the Declination Chart. Together the Map & Compass is then turned until the needle completely covers, or "Boxes" in the Magnetic Declination arrow on the Declination Chart. The map is now oriented to the lay of the land. This must be done every time magnetic bearings are to be taken with a simple compass.
Some of the drawbacks to the Magnetic Method, are that the Declination Chart line is only 1 inch long. A slight misalignment of a line drawn squarely across the Map, could result in a sizeable error.
Also, in the cases of very small degrees of declination, be sure to take the time to MEASURE the exact number of degrees the Declination Chart specifies, before drawing all these lines in. Sometimes the declination in an area is small, and Map makers exaggerate the visual Declination Chart for the sake of clarity. So measure the actual degrees along the center line of the map with the Compass Rose before drawing any lines.
Another problem is that a Topo Map is a picture of a Curved Surface, so straight lines drawn across it may be accurate in one corner, but off in another. The Navigational Chart for Lake Tahoe shows the Magnetic Declination as 15.75 at the southern end of the lake, and 16.25 at the northern end (in 1960). I'm talking about a lake that is only 20 miles long. That is about the same area covered by a 15 minute Topo. So drawing straight lines, on a 1x2 degree map, are going to be way off.
It occurs to me that the Magnetic North Method, without those lines, can't be used very accurately with every day car maps either. I need a method I can use with my Topo maps, AND every other map too...
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