The Compass

Component Parts of the Lightweight Compass

• Scale Ruler: Used to measure distances on the map.
• Magnifier: For helping to read small details on or cluttered areas of the map.
• Index Line: This is the point where you read of the bearing, this is also luminous.
• Direction of Travel Arrow: This must always point in the direction you wish to go.
• Orienteering Lines: These lines are used when applying bearings from and to the map.
• Magnetic Needle: The red half points to magnetic north, also has luminous marks.
• Romer Scales: To help plot and take grid references.
• Calibrations: From 0 to 360 degrees.
• Silicone Feet: To prevent the compass from sliding.
• Compass Housing: Sometimes called the bezel. A rotating dial marked in 2 degree increments.
• Clear Base Plate: Ideally you want a compass with a clear decent size base plate.

Tip: If at night you cannot see the luminous parts of the compass clearly, all you have to do, to illuminate them more, just switch your torch on and shine it onto the luminous parts of the compass.  The closer the torch to the compass the better the result.

Compass Maintenance

• Check for bubbles, if there is a bubble in a compass this will cause errors when taking bearings.  Normally heat will remove the bubble, ie, place the compass in a pocket, which is close to your body.  Leave it for a while and it should disappear. If not try leaving it in a warm room overnight and if the bubble is still there, then the compass needs to be replaced.
• Avoid handling a compass when you have just applied insect repellant, most repellants contain a chemical which reacts with plastic and causes it to become tacky.
• Check periodically or when the accuracy of the compass is in doubt to see if it is functioning correctly.
• Keep the compass away from electrical equipment this includes GPS units and mobile phones they could de-magnetise the compass.

How to Remagnetise your Compass

• Cover the compass housing with cling film to avoid scratching.
• Quickly stroke the south pole of a strong magnetic along the north point of the compass needle
• Repeat the north pole of the magnet along the south point of the compass needle. repeat the process until the needle settles.
• Check the compass is safe again by comparing with a compass you know to be correct.

The Mils Compass

The mils compass, is the main stay of the military due to it being more accurate than degrees.  There are 17 mils in 1 degree.

• North = 6400 mils
• East = 1600 mils
• South = 3200 mils
• West = 4800 mils

Normally the mils compass will also be marked in degrees on the inner side of the compass housing.

Prismatic Compass

This is proberly one of the best compasses you could obtain however can be very expensive, and as been used by the military for years.

Taking a bearing with a prismatic compass

Hold the compass in both hands with a thumb through the ring. The exact method of holding it is not important; find for yourself the best way to hold it steady. The lid must be vertical and the prism turned over into the reading position. Take care to hold the compass level; if it is tilted too much the card touches the glass and will not swing freely.

Look through the sighting slip and line up the hairline in the lid with the object on which the bearing is to be taken. At the same time look through the eye hole observe the readings on the card. When the card comes to rest read off the bearing against the hairline. A bearing to the nearest degree/mils can be read without difficulty. With practice and a steady hand a bearing can be read of to half or even a quarter of one degree.