How to use a compass – 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.
Compass basics – How to use a compass
What compass do we recommend? Suunto and Silva are good brands and we use the Suunto M3 Global at the Ultimate Navigation School. Get the best compass you can afford. The cheap ones on cards in petrol stations are usually inaccurate, the needle wobbles all over the place and we have even seen numbers wash off the bezel of cheap compasses in the rain!
Occasionally people forget and store their compass next to something magnetic like a car speaker in a door pocket which can reverse the polarity and it has to go back to the manufacturer. So, we always recommend before leaving the car park to do a sense check; is your compass’s red needle pointing north? Compare a direction from setting the map or ask other people in the group to point to north using their compass and check you all match.
Of course when you use your compass make sure you don’t have it near metal or magnetic items such as mobile phones, gates, bra under-wires, you haven’t attached to a metal carabiner, or you aren’t standing under pylons. Some ground areas have a lot of iron too such as Bow Fell in the Lakes which can send compasses off, so it can pay to research areas before you go, and to think about interference if your compass is misbehaving.
How to use a compass – So how do I take a bearing from the map?
Basically you are using the compass to measure an angle like a protractor. If you are at point A going to point B imagine this is a route line or your direction of travel. The compass will help you measure the angle between your route line and grid north on the map.
Let’s assume we are walking the first day of the Pennine Way. The mist comes down while we are having lunch at Wain Stones. We want to walk the path North East towards the Cairn and 630 contour marked on the map. This is an area notorious for people going off track so let’s use a compass bearing to follow the path N.E. for 260 metres from Wain Stones.
It’s important to mentally note the direction you are travelling in from your start at Wain Stones to your destination, as this is the direction you will need to lay your compass onto the map with the compass direction arrow (s) pointing the same way as you want to walk.
How to use a compass – Step 1.
Lay the compass on the map so the edge of the plate is cutting through your start, in this example Wain Stones, and your destination, in this case the path turning near the Cairn and 630 contour. It doesn’t matter where along the edge of your compass, as long as the edge of the compass cuts through both the start and destination. And that the direction arrows on the compass are pointing in the direction you want to walk.
How to use a compass – Step 2. Turn the bezel on the compass until the N on the bezel is pointing to the top of the map. (The writing on the map is the right way up to show the top). Looking through the compass bezel align the red orienting lines in the bezel so they are parallel with the blue North South grid lines on the map. (Interesting fact – North South longitudinal lines are called meridians).
You may have to slide the compass about a bit to see a grid line through the bezel. Just keep checking the edge of the plate is still cutting through your start and destination.
Twist the bezel until you have the red lines as parallel as you can with the blue North South grid lines on the map.
How to use a compass – Step 3. Read off the bearing next to the index line / bearing indicator on the compass. (The notches on the Suunto and Silva compasses are usually 2 degrees.)
This compass is showing 055 degrees.
You have now taken a grid bearing so this is 055 degrees grid!
How to use a compass – Step 4.You have taken a bearing relative to grid north on your map, but all compasses actually point to magnetic north, the point at which the earth’s magnetic field is focused. Magnetic North moves a fraction every year and in the UK it is currently approximately between zero and 2 degrees west of grid north. In the Alps it is around 4 degrees and in the United States varies up to around 15 degrees. So the thing to remember is wherever you are adjust for the local difference between grid north and magnetic north. (This is called the Grid Magnetic Angle or GMA).
The British Geological Survey website will tell you the GMA for your area http://www.geomag.bgs.ac.uk/data_service/models_compass/gma_calc.html
In the Peak District in 2018 it is around 1.25 degrees. So we adjust using a phrase to remember which way to add or subtract the GMA – ‘Grid to Mag Add. Mag to Grid get Rid’
So to our grid bearing of 055 degrees we add 1.25 degrees to get the magnetic bearing. Turn the bezel to add 1.25 (just over half of one notch as a notch is 2 degrees on most Suunto and Silva compasses). That gives us 056 degrees magnetic.
We can now follow the compass accurately.
How to use a compass – Step 5. Leaving thebezel alone, hold the compass flat and turn your whole body around slowly until the red orienting lines in the bezel align with the floating red North. Remember this with ‘Put Red Fred in his bed’. You’d be amazed how many tired experts occasionally use the white end of the needle in error, hence the phrase to remind you to use the red end.
Looking ahead if there is a feature on your bearing you can see, put the compass down and walk to that feature, then check the direction again. If you are not so lucky or it is misty, you will have to keep stopping and checking the compass direction arrows with Red Fred in his bed.
Remember though that this is the direction from A to B. If you wander sideways off track your bearing will not work. You have to try to stick to your original direction line, easier said than done on rough ground, but that is for another article.
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. In our example it will point along the path to the path junction near the cairn and 630 contour line.
Ultimate Navigation, Ordnance Survey and TRAIL magazine.
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