Compass Glossary

Azimuth Housing: The white housing with the knurled edges on your compass which holds the clear liquid-filled capsule. The housing rotates within the compass base for taking or setting bearings.

Bearing: The direction from one location to another location given as a reading in degrees.

Capsule: The sealed unit which houses the magnetised needle and the clear fluid which dampens or slows the needle from spinning.

Clinometer: This feature is found on the 15TD-CL, 25TD-CL/E and Voyager 8040 compasses. It allows the compass to measure vertical angles like the slope of a hill. It can also be used as a level.

Declination: Simply stated, declination (or variation) is the error between true North (which is what all maps are based on), and magnetic North (which is what all magnetic compass needles point to). The declination angle is different all over the world. In Australia it varies by as much as 18 degrees from coast to coast.

Graduated Dial (or “Azimuth Ring”): This is the white dial with the zero to 360 degree markings.

Gun Type Sights: As its name implies these are used like gun sights for sighting and taking bearings.

Index Line: The mark on the front sight where you read a bearing on your compass.

Line of Travel: Actually the same as the sighting line. This line or arrow, points you in the direction you need to go to get to your desired destination.

Liquid Damping: Liquid damping allows the needle to come to a rest quickly, allowing for faster readings. Cheaper compasses which do not use this system are often times inaccurate and the needle tends to move “forever”. Silva uses a mineral spirit base fluid in its capsule because it will not freeze or boil and has predictable thermo-dynamics. The liquid filled capsule has been tested to -40 and +50 degrees celsius and from 10,000 metres down to 60 metres below sea level, and to water depths of 10,000 metres!

Magnifier: Found on some models of compasses, these help the user read the small print on a map.

Mirror: This feature is found only on the Ranger 15 and 25 series and models 23, 26, 27 and Voyager 8040 compasses. It is used to make in-line sightings which is the most accurate method of using a hand held compass.

Orienteering: The sport of racing from one point to another while using a topo map and a compass. Courses are set up according to various levels of skill and age. Very popular in Europe and Australia.

Orienting Arrow: This is the red or black outlined arrow on the bottom of the clear, liquid filled capsule. Used with the red end of the magnetic needle north to determine your bearing or direction of travel.

Prismatic Compass: A compass with a mirror which allows the user to see both distant objects and the compass face at the same time. This is the most accurate type of hand held compass.

Protractor: Some models of compasses have this feature to allow the user more flexibility in using the compass with a map. Bearings can be more easily plotted with the protractor.

Sighting Line: This is the line you sight along to take a bearing.

Triangulation: A method of finding your location on a map by sighting on two or three visible land features. By plotting the known bearings you can find your location at the point where the lines intersect (see the compass instruction manual for a more complete definition and illustration).