How to use a compass

How to use a compass part two – Read our articles on how to use a compass, and other navigation tips in TRAIL magazine. Why not join us on a foundation or intermediate map and compass course?

We can use the compass not only to find a way from A to B in poor visibility, but also as another tool for locating our position. To do this you have to be confident with the basics and we get asked a lot on courses to refresh taking compass bearings in order to improve people’s confidence. Before heading onto the hills, ensure you know how to use a compass.

How to use a compass – So how do I take a bearing from a ground feature?

You are confident with the basics and can take a bearing from the map. But what about ground features?

We can use ground feature bearings to navigate from A to B but also to help us relocate.

Taking a compass bearing from a ground feature

How to use a compass – Step 1.

Let’s assume initially you want to walk to a hill in the distance along a saddle and you are worried the mist is about to come in.

Choose a clear point at the feature to aim at e.g a trig point or summit so you have a clear aiming point. Lay the compass flat on your hand with the direction arrows pointing towards your feature. You may find it easier to get down on one knee and lay the compass flat on your upright knee.

Lift the compass up and closing one eye, aim the direction arrow at your feature.

How to use a compass -Step 2.

Bring the compass straight down and looking down onto it turn the bezel and put the red orienting North lines in the bezel in line with the red floating North needle. Use the saying ‘Put Red Fred in his bed’ to remember which end of the needle you want if you wish. Check it is as aligned as you can get it. Looking straight down on top of the compass helps stop parallax error.

Now lift the compass straight up and check the direction arrows are still pointing at your feature. Bring it back down and looking down recheck the red orienting North lines in the bezel are still aligned with the red floating North needle. Adjust the bezel if it is not perfectly aligned. You may need to do this a few times to get it spot on.

Now read off the number on the bezel next to the index line. This is your magnetic bearing and in the picture is 055 degrees.

To walk on this bearing simply hold the compass flat and turn your body around until the red North needle in your compass is still aligned with the red orienting North line in the bezel. The direction arrows on the compass now point to your target feature as you walk.

Remember this bearing is only good if you are walking in a straight line from A to B. If you wander sideways off track you will have to take another bearing or walk back to your original track to follow your bearing. (We can describe some advanced techniques for that in a later article.)

What else can I do with ground bearings?

Ground bearings are a very useful tool to aid in relocation. In most techniques the approach is to take a bearing from a known ground feature in the distance, then draw that bearing line on the map.

How to use a compass Step 1. Take a ground bearing. Point the compass direction arrow(s) at the feature and turn the compass bezel until the red North floating needle is in the red orienting North lines in the bezel. Read off the bearing number against the index line on the compass base plate. This is a magnetic bearing.

How to use a compass Step 2. Convert your magnetic bearing to a grid bearing. (Remember Grid to Mag add, Mag to Grid get rid). So in the Peak District in 2018 we get rid (subtract) 1.25 degrees off your magnetic bearing to get a grid bearing. Adjust the bezel so you subtract 1.25 degrees off the number you read at the index line. (Turn just over half of one notch as a notch is 2 degrees).

How to use a compass Step 3. Lay the compass on the map so the edge cuts through the feature you took the bearing off on the map. Make sure the direction arrow on the compass is pointing from your position towards the feature on the map.
Leave the bezel set where it is, but swivel the whole compass on the map until the red orienting lines in the bezel are aligned with the North South grid lines on the map. Get the lines as exactly parallel as you can by moving the whole compass, don’t change the bezel position. Check the edge is still cutting through the feature you took the bearing off.

How to use a compass Step 4. Draw a line along the edge of the compass from the feature towards your location. You are somewhere along that line.

To get an accurate fix you need to do two or three bearings on different features (preferably ones about 120 degrees apart) and lay those onto the map. Where they cross is your position. This technique is called resection.

Resection is useful on say a wide open moor with no features to get a fix on your position, as long as you can see three distinct features to take bearings from. But there are some more very useful techniques for using ground bearings.

How to use a compass – Transit lines

Say you are walking along a path and want to know how far along you are. Take a ground bearing off a feature at right angles to you and lay that onto the map. Where the path and this line cross, is where you are.

You can also adapt this technique. Say you want to know when you have reached a point on the map and get a fix. Take a map bearing from the point you want to get a fix at, to a feature you know you will be able to see off to one side of your route, say a wood or hill top. Convert your map grid bearing to a magnetic bearing and set your compass. This is the bearing that will show you when you are abeam your fix point.

Walk in a straight line to your fix point (it is handy to have a second compass or friend to walk on a bearing to your fix point). On your compass, when the red floating North needle swings round into the red orienting North lines in the bezel, and it exactly aligns, you know you have reached your fix point.

How to use a compass Step 4. Draw a line along the edge of the compass from the feature towards your location. You are somewhere along that line.

How to use a compass – Watch the Ultimate Nav video here – https://youtu.be/HYsF_EXzEzQ

Looking over the top and down onto your compass to avoid parallax (error due to your viewing angle), check Red Fred is in his bed, then look at the direction your compass’s direction arrows are pointing. That is your direction to travel.

Ultimate Navigation, Ordnance Survey and TRAIL magazine.

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