Using a compass

A simple baseplate compass works anywhere, needs no battery and is light enough to carry every time. Combined with a map, it lets you travel in a straight line even in fog, forest or darkness.

Parts of the compass

• Baseplate: the clear plastic base, with a direction-of-travel arrow at the front.
• Housing: the rotating dial marked in degrees from 0 to 360.
• Orienting arrow and lines: printed inside the housing.
• Needle: the red end points to magnetic north.

Taking a bearing from the map

1. Lay the compass on the map with the long edge joining where you are to where you want to go. The direction-of-travel arrow must point towards your destination.
2. Turn the housing until the orienting lines run parallel to the north–south grid lines, with the orienting arrow pointing to the top of the map.
3. Read the bearing where the housing meets the direction-of-travel arrow.
4. Adjust for magnetic variation if needed (see below).

Walking on a bearing

1. Hold the compass flat in front of you, at waist height, with the direction-of-travel arrow pointing straight ahead.
2. Turn your whole body until the red end of the needle sits inside the orienting arrow. People often say "put red in the shed".
3. Look along the arrow and pick a landmark — a tree, rock or bush — in that line.
4. Walk to it, then repeat with the next landmark.

Magnetic variation

Magnetic north and the north of the map grid are not quite the same. The difference, called declination or variation, depends on where you are and changes slowly over the years. The map margin usually states it. In some areas it is so small you can ignore it; in others it is large enough to send you well off course over a few kilometres. Add or subtract it as your map explains.

Keep it accurate

• Keep the compass away from metal, magnets, phones, car bodies and power lines. They can pull the needle.
• Hold it level so the needle swings freely.
• Check your bearing often, not just at the start.

Back bearings

To return the way you came, add 180 to your bearing (or subtract 180 if it's over 180). Or simply walk with the white end of the needle in the orienting arrow.

Using the phone

The app's compass mode shows an arrow to your chosen waypoint on a dim screen to save battery. Calibrate it by moving the phone in a figure of eight when asked. Still carry a real compass: a phone can run flat, and a baseplate compass never will.

This article is in the Grid Survivor app, searchable with no signal. Get the app · £4.99