There is a particular kind of silence that falls over the hills when cloud comes down. Sound flattens, colour drains away, and the ridge you could read perfectly ten minutes ago becomes a blank grey-white wall. Landmarks vanish, paths dissolve into bog, and the map alone tells you almost nothing about which way you are facing. This is the moment your compass stops being spare kit and becomes the thing that gets you off the hill.

Learn the instrument before you need it

A baseplate compass is a simple thing, but it only works if your hands know it without thinking. Spend half an hour on a familiar path in clear weather, and the parts will become second nature.

• The baseplate — the transparent rectangle, with a direction of travel arrow along one edge.
• The bezel — the rotating housing marked in degrees, turned by hand.
• The orienting lines and orienting arrow — inside the bezel, used to line the compass up with the map's grid.
• The magnetic needle — the red end always swings to magnetic north.
• The index line — the mark at the top of the bezel where you read the bearing.

British hills sit close enough to magnetic north that the difference from grid north is small — usually a degree or two — so for walking purposes you can generally ignore it. Do check the margin of your map if you are heading somewhere far from home, and remember that compasses dislike being stored next to phones, magnets or steel buckles.

Taking a bearing from the map

A bearing is simply a direction expressed as a number of degrees, measured clockwise from north. To transfer one from paper to hillside:

• Lay the compass on the map with its long edge joining where you are to where you want to be, direction of travel arrow pointing at your destination.
• Hold the baseplate still and rotate the bezel until the orienting lines run parallel with the vertical blue grid lines on the map, with the orienting arrow pointing to the top of the map.
• Read the number at the index line. That is your grid bearing.
• Lift the compass, hold it flat at waist height, and turn your whole body until the red end of the needle sits inside the orienting arrow — "red in the shed".
• The direction of travel arrow now points along your bearing. Pick a feature along that line, even if it is only a patch of heather thirty metres away, and walk to it.

Repeat that last step indefinitely. Long legs on a bearing are how people drift; short ones keep you honest.

Walking the line in thick weather

Human beings veer. Give anyone a hundred metres of featureless ground and they will curve, usually to one side, without ever noticing. The cure is to check the compass every twenty or thirty paces, bring the needle back into the shed, and carry on. Keep the compass in front of you rather than dangling at your side, and resist the temptation to walk on a remembered direction instead of a checked one.

Two techniques save a great deal of time when visibility is poor. Aiming off means deliberately steering a few degrees to one side of your target so that you meet a linear feature — a wall, a stream, a forestry edge — and know for certain which way to turn along it. An attack point is an obvious feature close to your destination: aim for that, then navigate the final leg precisely. Both beat wandering around a summit plateau hoping to bump into a cairn.

Counting paces and timing your legs

Distance matters as much as direction, and in mist there is nothing to measure it against. Pace counting fills the gap. Walk a measured hundred metres on flat ground and count every time your left foot lands — most adults find this lands somewhere between 60 and 70 double paces, though a heavy pack, bog or steep ground will shorten your stride considerably.

Keep count with beads on a cord, by transferring pebbles between pockets, or simply by muttering in blocks of ten. Then check the result against timing: roughly 4 kilometres an hour on rough hill ground, plus about a minute for every 10 metres of ascent. When pacing and timing agree, your position is a good deal more reliable than a guess.

Stop and confirm your position

Navigation in poor visibility is a series of small confirmations rather than one big leap of faith. Every few hundred metres, or whenever the ground changes underfoot, stop and ask where you must be. Use catching features — the fence you should cross, the stream you should meet, the corner of plantation you should skirt — and tick them off as they arrive.

If something does not match, stop immediately. Wandering onwards in the hope that the mist will lift is how small errors become long days. Turn the map so it agrees with the ground using the compass, take a back bearing along the line you have walked, and look for a handrail — a wall, a stream, a ridgeline — to follow until a known point appears. With a bearing, a pace count and the patience to check both, the cloud can take the view but it cannot take your position.