Used under GNU Free Documentation license. © Romary

Choosing a compass

Choose your compass with care. The most appropriate type for use in scouting is probably the orienteering compass. A good one will have a well balanced steel magnetic needle that settles into position quickly. The needle should be coloured differently at each end, usually red at the north end. If the tip glows in the dark then even better.

The base plate and dial are usually strong plastic. The dial will have increments of around 2° marked clearly. On the dial itself will be faint meridian lines (faint parallel blue lines pointing in the same direction as north on the dial). Some even have extra information such as magnetic variation or declination degrees marked on the dial. The dial also has an arrow marked on the bottom aligned with north on the dial.

The base plate should be transparent and have scales in both metric (cm and mm) and imperial (inches). A magnifying glass, clinometer, sighting mirror and adjustable declination screw are all welcome extras.

Don't forget a strong strap attached to the base plate which should be securely held at the other end to your shirt pocket buttonhole or around your neck.

There are several different types of compass available. These may range from the simple 'toy' compass which has a fixed dial to the more technical prismatic compass. Here we will concentrate on the most suitable compass for scouting, the orienteering type compass.

Typical compass

A typical (Silva type) compass consists of a magnetic strip of metal, suspended or pivoted (so it can swing freely) within a moveable dial. The dial is usually liquid filled (this dampens the oscillation of the needle allowing it to settle into position much more quickly) and has several parallel lines marked on the dial itself. The compass should have a clear plastic base plate with straight edges. Along the edges should be scales in both metric (cm and mm) and imperial (inches). Some may have additional features such as a magnifying area and degrees of declination/magnetic variation (usually marked on the compass dial). A wrist strap is another important feature if you want to keep the compass.

There are usually 3 different types of arrow marked on the compass. As indicated in the diagram, the vertical arrow marked on the plastic background is your direction of travel arrow. This is the only arrow you ever follow.

The arrow that spins in the middle of the compass (usually coloured red and white) always turns to point north (the red end is the end that points north). NEVER follow this arrow (because you will always be walking north then, no matter where you actually wanted to go!) When using a compass try not to hold it near any metal or any magnets else this arrow will be attracted to them and you will end up going in the wrong direction. Depending on where you are simply placing the compass near the floor may give you an inaccurate reading due to iron and mineral deposits in the ground. Always check you have the same reading at ground level and when standing up.

The third arrow is the one that will be marked upon the dial. (you cant actually see this on the picture). It is usually a red arrow marked on the bottom of the dial. This is the one that will match up with the red and white pointer that spins. When you want to read a number off the dial, look at the point where it touches the line at the top (the one marked by ‘read bearing here’), this is the number you want.

NOTE: There are 360 degrees in a circle. Be careful about how many degrees each line on the compass represents. Normally on compasses of this type each line is ‘worth’ 2 degrees. This is important as a difference of 5 degrees over a walk of 6 miles will mean you will be about half a mile from where you should be!