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Basic Features of A Compass

Have you ever tried to look into your compass and thought what is inside of it? Sometimes, it is good to know the basics of a certain item. This way you would understand how it works and what is the purpose of each fragment that makes up the whole tool. Who knows? This information might come in handy like when you get lost while backpacking and the only choice you have is to build one yourself! Below are the basic features of a compass.

Basic Compass Featurescompass

Backpackers customarily use what is known as a “base plate” or “orienting” compass. (“Orienting” refers to the act of determining your exact position; “navigation” is the process of determining your destination and guiding yourself toward that objective.)

The most common features of a basic compass include:

Magnetized needle: Usually the red end of a pivoting compass needle. This end points to the strongest magnetic field, which is usually the magnetic North Pole. “Magnetic north” is different from “true north”—the geographic North Pole, where all longitude lines meet. Magnetic north, one of earth’s 2 magnetic poles, lies in an island chain within the Canadian Arctic. True north and magnetic north are separated by more than 1,000 miles. When working with a map, you must compensate for the difference between true and magnetic north. This can be accomplished in various ways. Keep reading below for some tips or check out the REI Expert Advice discussion on Adjustable Declination in a Compass.

Liquid-filled capsule: The housing (or dial) that contains the needle and damping fluid. This nonfreezing fluid slows a needle’s jiggling and brings it to rest quicker than an air-filled housing. At high elevations or in cold temperatures, the liquid may contract and create a bubble. A bubble will not impact accuracy. Bubbles disappear when a compass is returned to normal conditions.

Rotating bezel (or azimuth ring): A ring marked with degrees from 0 to 360 (preferably in 2° increments) that encircles the outer edge of the compass capsule. The smaller the interval of degrees on the bezel, the easier it is to take an accurate bearing. The bearing or “azimuth” is the direction you wish to travel (expressed in degrees); it is an angle relative to north.

Base plate and ruler: The base plate is a rectangular, transparent base where the capsule sits. Better compasses have rulers (in inches and centimeters) etched into the “straight edges” of the plate. These are helpful when measuring distances on a map. Try to select a compass that offers scales you are likely to use. Common topographic map scales are 1:24,000 (used by the USGS)and 1:250,000. A long straight edge is helpful for drawing bearings on a map.

Orienting arrow and parallel meridian lines (or, north-south lines): Located on the bottom of the compass housing. The nonmagnetic arrow’s directional end is usually red and, coupled with the meridian lines (which you align with the north-south lines on a topographic map), helps orient the compass to the map.

Index line or direction-of-travel line: Located at one end of the base plate. This is the point of the compass dial at which you set or read your bearing measurement.

Get your compass and try to point out each feature. You may have an advanced compass or a traditional one, either way you will still find these basic features – except of course if you have a digital one. This is added knowledge and you can even make a camping game out of it. It’s always fun learning in camp you just have to be creative.

Read more about advanced compass features at Rei’s website.

Image source: Vivian Evans