Compass Anatomy

A description of the basic parts of a compass

There are many different types of compasses, but for bushwalking, it’s important to get a unit that can reliably measure bearings and help the user determine their travel route.

While all compasses are made up of the same general anatomy – a baseplate with arrows in the direction of travel, a rotating bezel with degrees markings, and a magnetic needle held within a housing unit with orienting lines on it – compasses also have a number of additional features like mirrors that may be appealing to some users.

Beware of cheap substitutes like compasses on keyrings and toy units. Spend the money for something that is lightweight, compact and reliable.


Basic Features:

1 Baseplate: The transparent panel on the base of the compass. Usually with ‘direction of travel arrow’ for orientation and ruler markings for calculating distances. The direction of travel arrow points in the direction you need to travel after setting a bearing.

2 Azimuth ring/rotating bezel: This rotating bezel has degrees markings from 0 to 359° around the outer edge, and encircles the needle capsule. The finer the scale, the more precise the navigation can be.

3 Magnetised needle: A black and red needle usually suspended in a damping fluid to help steady the movement. The needle spins freely on a mid-axis and the red end settles pointing towards the north magnetic pole.

4 Needle housing with orienting lines and arrow: Needle housing contains magnetised needle and damping fluid. It has orienting lines that can be aligned with the vertical grid lines on a map.
The orienting arrow is aligned with 0° or North on the housing.

5 Index line: The index line is an extension of the direction of travel line. It is fixed and marks any bearing that has been set by rotating the compass housing.

6 Magnifying glass: for more detailed reading of map features

7 Declination adjustment: Some compasses have a declination adjustment feature where it’s possible to adjust the “declination” (ie. the difference between true north and magnetic) to match the area you are walking in. Thus, for every measurement, you don’t need to account for declination, rather instead, it’s taken into account for you. This works well if you are regularly using your compass in one area, and only need to reset it when you travel to a new area.

8 Sighting mirror: Can be helpful to aim more precisely for a distant landmark, especially in open terrain. Mirror can also double as an emergency aid for signally.

9 Global needle: Standard compasses only work in one hemisphere, so they are either northern or southern hemisphere specific. More expensive models can work in both hemispheres and therefore function well worldwide.