Navigation - Compass Basics

This picture shows my primary compass (I have a button compass as backup).

The first thing I want to mention is that the lanyard (rope) is attached to a cover and that this cover fits onto my belt. I always carry my compass in such a way as it is convenient and so that it will not get lost.

Of all the navigation aids that I might carry the compass is the most important.

A Type 4 compass contains all the essential features required to take readings from a map and to navigate in any terrain. It is not a sighting compass but can be used as such for practical purposes. My compass was bought in the UK and contains 3 standard scales for maps - 1:25,000, 1:50,000 and 1:63,360 (1 inch to 1 mile). When all else fails there is a rule.

Compass Overview

Now it is time to look at the individual parts of a compass.

Technically, the compass is the needle in the middle. This is enclosed in a fluid-filled compass housing which is in turn attached to a base plate.

Base Plate

This is the bulk of the compass. It has printed on it a lot of different map scales for the various maps that you are likely to be using.

Printed on the base plate is a single arrow which above it has a flourescent line. This is called 'Direction of Travel'. It is used to navigate (see below).

Underneath it are 3 rubber feet. These make it easy to place the compass on a map and keep it there while you take a reading.

Finally, this particular base plate includes a magnifying glass.

Compass Housing

The compass housing is the heart of the compass. The base of the housing has parallel red and black lines printed on it. These are used to line up with the grid lines on a compass - it makes life easier. It also has one big red hollow arrow painted on the bottom that is parallel to the red and black lines.

The Convention is that red points towards North and Black towards South.

Finally, and most importantly the outer edge of the compass housing is printed with N-S-E-W and bearings from 0-359. These are used for transferring bearings to and from a map.

Compass Needle

This particular model has a red North needle and a white South needle. The North point on the needle also has a blob of flourescent material. The needle can move horizontally but not vertically. The fluid in the compass housing damps down any movement caused by holding the compass.

Using a Compass

Warnings

The first thing to be aware of is that a compass will not be 100% reliable. They can be quite sensitive to other devices that have strong magnetic fields such as your mobile phone.

Sometimes the terrain can be a problem. If the underlying rock contains lots of iron then it can throw off the compass. This is very rare but it can happen. Really, the thing to be aware of is that a compass must be treated as less than perfect - what it says may not be always gospel.

If you are the least bit concerned that the compass is unreliable then all you need to do is to walk 30 or 50 metres away from where you are and try again. This will prove if their is a terrain issue.

How to chase a bearing

Let's assume for now that you have taken a reading from a map and are ready to travel. [XXXXXXX LINK]. The rest is now simple!

You hold the compass in your hand in such a way as you can see the compass and the countryside and with the 'Direction of Travel' arrow pointing where you want to go. Now turn your body until the red arrow of the compass aligns with the red arrow on the base of the compass housing.

You now walk forward in the direction of the 'Direction of Travel' arrow whilst ensuring that the compass arrow aligns with the red arrow on the base of the housing (as shown above).

The needle may jump around a little but that is OK.

Summary

How to use a compass with a map will be discussed elsewhere.