Compass (magnetic compass) is a basic navigation device that uses the earth’s magnetic poles to point a magnetized needle towards the north pole. A compass works because the earth’s rotation (and some theories add that the molten lava in the Earth’s crust) create 2 magnetic poles that allow a magnet (the compass needle) to be attracted to the opposite poles – so when a compass points north it is actually aiming for the southern magnetic field. But, to keep it simple, the needle with the mark N will point to the north.
This quality of the compass means that you can create a compass with any magnetized needle on a low friction rotation axle – we all know the needle on a floating leaf trick and it actually works, but you need to create the right current, otherwise you will end up with the needle pointing south (polarization).
The biggest negative aspect of the compass’ simplicity is its sensitivity – any electromagnetic current, metallic object or magnet might disturb a magnet and create a distortion. This distortion can be extremely dangerous in navigation situations as distances can be long and the mistake huge – when using a compass there need to be no metallic objects, magnets or live currents near by. The best solution is usually putting the map and compass on the ground and orient them there, away from you and everything that you are carrying.
Every compass will have one thing, always:
The needle is the heart of the compass and will have a clear mark of the side that points north, usually using the letter N and might be coloured – mostly in red. Modern compasses have the needle in a housing (2) that holdes the needle and a liquid. The liquid is there to allow smooth movement for the needle, increasing the sensitivity of the needle to point to the right (northern) direction.
Beyond the needle compasses will vary, but most will have:
Azimuth/Bearing dial (3) – shows 360° marked on the dial that is mounted on the needle housing. This dial allows the user to set an azimuth/bearing in combination with the needle.
Orienting lines (4) – lines marked in the housing to be aligned with maps eastings to be able to set bearings or calculate returning bearings.
Orienting arrow (5) – an arrow marked in the needle housing to align the bearing dial with the north.
Land navigation compasses will also include:
Base plate (6) – holds the needle housing and have several markings including a ruler (7) to measure scale.
Direction Of Travel (DOT) arrow (8) – printed on the base plate and parallel to it, the DOT is used to follow the direction you want (based on a set bearing) or to get a bearing from a land feature.
Index line (9) – printed line on the bearing dial that is used to follow a bearing when aligned with the DOT arrow.
Scales (10) – can be used to measure distance on a map based on the map’s scale.
Army compasses (that are used a lot) will have:
Sight (11) – used to increase accuracy when following a bearing on the compass.
Lens (12) – helps to see the compass dial and needle when used in 30° angle from the top.
The compass is a powerful tool when used right and an extremely dangerous if not. Getting your direction wrong on a longer distance can lead to being miles off your intended location. Learn how to use your map and the compass well and it will work like a charm.
To make sure you are ready to tackle compass reading, make sure you are happy with your map reading skills first.
Do you have any other compasses you use when going out?