Compass FAQs

7/25/2019 Compass FAQs

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If you don't find the answers you are looking for here, you mightwant to check out our learning section back on the home page.

What should I look for in a good compass?How do I use a compass?What is a reciprocal scale?What is the compass mirror used for?Do I need a Global Needle if I will only be in the US?What are the "cotangent" tables on the KB-14 sighting compass used for?

What should I look for in a compass?Accuracy and durability should be paramount in your quest for a good c ompass. The easiest way to determine reliability may be

the brand (The most dependable brands are Suunto, Silva, and Brunton). While the brand is definitely a good indication of quality,each manufacturer supplies compasses of varying grades including various features. When it comes to choosing a specif iccompass you will want to consider the following:

Bezel resolution (5 degree, 2 degree, 1 degree, 1/2 degree -- lower is better)Compass accuracy (again lower is better)Dampening time (how long it takes the needle to settle)Capsule temperature range (don't let the cold weather get you lost)Translucent baseplate? (this is helpful when working with maps)Sighting mirror? (this feature can allow more accurate readings to be taken)Declination scale? (helpful for quick declination calculations)

Adjustable declination? (eliminate the need f or c alculation altogether)Clinometer? (for determining slopes or heights)Reciprocal Scale? (very helpful for sighting compasses. not necessary for others)

How do I use a compass?We have developed an entire page on how to use a map and compass. If t he extent of your knowledge stops at "the needle pointNorth", you should be sure to check our our "How To Use A Map & Compass" page. And once you begin to work with a compassyou will quickly want to learn what exactly declination is, how to find your declination value, and how to use your declination value

What is a reciprocal scale?The reciprocal scale is often called the reverse scale, because the reciprocal direction is the exact opposite of the direction you arheading. The reverse/reciprocal scale is v ery useful in determining your location on a map. For example: if you see that mountaintop "A" is at a bearing of 240 degrees from you (the reciprocal is 60 degrees), and t he bluff is at a bearing of 300 degrees from you(the reciprocal is 120 degrees), you can draw a line on your map from the mountain top "A" in the di rection of 60 degrees, and a linfrom the bluff at 120 degrees. Where these lines intersect is the location you are standing. Reciprocals are easy to get from abaseplate or mirror compass, because you just look at the white tail of the needle and read the reverse direction. Since you can'tdo that when looking through a sighting compass the smaller reciprocal scale is very helpful.

What is the compass mirror used for?The compass mirror allows the user to view the target and the compass capsule at the same time. This is why we group mirrorcompasses in the sighting compass family -- as you can "sight" your target and your bearing at the same time. See our compassmirror page for more details.

Do I need a Global Needle if I will only be in the US? Without a doubt, the greatest benefit of t he Global Needle is the capability of it's worldwide use. As a result of t he design howevethere is a secondary benefit. The way the Global Needle is capable of handling worldwide magnetic zones is with it 's ability tohandle needle tilts of up to 20 degrees. This characteristic is great for hiking because it means as you bounce along the trail, youdon't need to have the compass perfectly level to get an accurate reading... making it easier to get readings while you are walkingTo learn more about the Suunto's patented Global Needle, see our " What is a Global Needle?" page.

What are the "cotangent" tables on the KB-14 sighting compass used for? The cotangent table is helpful for determining your distance from specific objects. First , lets talk about Figure A. Assume that wit
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the map, you can determine the relationships between the location of the house and the tree, but you aren't sure your exactlocation. Use the map to determine the distance of that short perpendicular line from the house to the line going towards the tree. you take that distance and multiply it by the cotangent of 20 degrees (the angle you determined with your compass), that will tellyou distance between you and the house. And since you probably don't know the cotangent of 20 degrees by memory, you justhave to refer to the handy cotangent table on the back of your KB-14.

Figure B show a more realistic and typical situation. First, y ou would pick two objects in the horizon that seem as best you can te

to be roughly side by side. If you can determine the angle between the two objects with your compass (let's say it was 4 degreesand you know from your map that those two objects are 1/2 mile apart, then you just perform this equation:

(cotangent of 4 degrees) X (1/2 mile) = your aprox distance to the house or mountain....and since the scale on the KB-14 says the cotangent of 4 degrees is 14.30, you can calculate...(14.30) x (1/2) = 7.15 miles to the mountain.

Figure A is a more accurate depiction of the proper geometric properties, but it is a little unrealistic to assume you can determinethe distance of that cot angent line with great accuracy, since you don't know your own exact location. Figure B is a more realist icexample of how to use a cotangent to approximate your distance to a destination.

FREE Newsletter / What is a Global Needle? / How To Use A Map & Compass / What is Declination?Find Your Declination Value / How To Use Your Declination Value / Compasses with adjustable declination.

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