Estimating direction with a wristwatch (very imprecise)

The sun appears to travel once around the Earth in 24 hours, so about 15 degrees per hour. The hour hand of a watch, however, goes round once in 12 hours, twice as fast. That is why you halve the angle between the hour hand and 12: this cancels out the hand's double speed.

The method rests on an assumption: that the sun is due south (northern hemisphere) or due north (southern hemisphere) at 12 o'clock by the clock. That is only roughly true. Clock time applies to a whole time zone, but the sun pays no attention to time zones: at the eastern edge of a zone it reaches south earlier than at the western edge. Add daylight saving time, which shifts everything by an hour, and a small seasonal variation in the sun's path.

In the southern hemisphere you reverse the method: point 12 at the sun, and the line halfway between 12 and the hour hand points roughly north. If you do not know which hemisphere you are in, you cannot use the method sensibly.

The watch method is most usable in mid-latitudes (for example in Europe), in the morning or afternoon when the sun is not too high. Then it can help you roughly confirm a direction: 'So the valley I want lies roughly to the west – does that match my map?'

Around midday it becomes very imprecise, because the angle between the hand and 12 is small and every little error has a big effect. In the tropics and near the equator it is hardly usable: there the sun stands almost straight overhead at midday, and depending on the season it can even be in the north rather than the south at noon. Under an overcast sky the method does not work at all.

A digital watch or a phone also works: draw a clock face showing the current time on a scrap of paper or on the ground and use it the same way.

Hold the watch level, otherwise the direction of the hand will not match the direction of the sun. Never look straight into the sun. A trick helps: hold a thin stalk or stick upright at the tip of the hour hand and turn the watch until its shadow falls exactly along the hand towards the centre – then the hand points at the sun.

Do not forget daylight saving time: it is the most common mistake. And treat the result as a rough estimate. Compare it with other clues: where did the sun rise this morning? Where does a shadow stick point if you watch it for a while? What does the terrain say? Only when several clues agree do you have a usable direction.

The biggest danger of the watch method is false confidence. Because it looks so simple, it is easy to think the result is precise. Over a long distance, an error that looks small at the start can take you far from your target. So never navigate long distances or into steep, unknown terrain by the watch alone.

If you are lost, a rough compass direction is often not the most important thing. First stop, calm down, clarify your position as well as you can and, if there is danger, get help (local emergency number, 112 in the EU). The direction can then help you head for a large, safe handrail.

The watch method appears in many survival manuals – almost always with a note that it is imprecise. More accurate without a compass is the shadow stick, watched over a longer period, or the North Star at night. Most reliable of all, though, is simply always carrying a small compass.

A good exercise: try the method at home at different times of day and compare it with a compass each time. That way you see for yourself when it is usable and when it is well off.