A mountain expert has outlined a problem affecting one of the hillwalker’s most trusted instruments, and one vital for navigation in poor visibility.
Heather Morning, mountain safety advisor for the Mountaineering Council of Scotland points out that a compass’ needle can be afflicted by reversed polarity, with potentially lethal consequences.
Ms Morning said navigation errors are the cause of many calls for mountain rescue, but walkers may be misled by an instrument in which they place their faith.
The needle of a compass can flip so that, instead of pointing to magnetic North, it actually points south.
Ms Morning said, if this happens and the hillgoer is unaware, the consequences can be serious.
She said: “Picture the scene: you are out on the hill alone, ticking off that remote munro.
“Unexpectedly the mist descends and you find yourself in poor visibility. Undeterred, you continue onwards and upwards.
“Navigation is easy; you are ascending a defined ridge which leads onto a broad summit plateau which gently rises to the summit over a shattered boulder field.
“Descent however, is a little more challenging, the underfoot conditions mean that the normal defined munrobaggers’ path has not developed; a compass bearing is required to locate the descent ridge.
“As usual, your compass is sensibly attached to the zip in the chest pocket of your waterproof jacket, the same pocket where you put your mobile phone.
“Taking a bearing to the top of the ridge, you start heading down. Alarm bells start to ring as the ground ahead seems to be dropping far more steeply than you remembered on the ascent.
“Suddenly out of the mist, the ground drops dramatically in front of you over what looks to be quite a significant crag. You stop to re-asses.
“Imagine if this had been winter and the ground was snow covered; how easy it would have been to walk right over the edge.
“It would be easy to assume that it was you who had made the mistake, but in the scenario above the compass had been affected by the magnet in your mobile phone case and the north-south needle had been reversed, resulting in a bearing that took you in completely the wrong direction.”
Ms Morning, who is also a mountain rescue team member and search dog handler, said many modern gadgets are capable of affecting compasses. These include mobile- and smartphones, magnets hidden inside mobile-phone cases, avalanche transceivers, radios, personal locator beacons, GPS units, cameras, car keys, small magnets on belt fastenings, and even underwired bras.
The mountain safety expert said even if your needle doesn’t flip completely, it may become sluggish and slow to settle if it has been partially reversed.
It is important to keep the compass away from potential sources of magnetism both on the hill and in the home.
If a compass has been affected, it is possible to ‘stroke’ it back to correct polarity by running a strong magnet outwards along the north end of the needle.
Ms Morning also pointed out that Silva, one of the main manufacturers of compasses, will remagnetise one of its flipped compasses if you return it to them, no matter how old it is.
She cautions against attempting to use a reversed magnet. “In my personal experience – this problem has happened to me three times in the past 12 months – the needle does not invert by exactly 180 degrees.
“It would appear to be approximately 10 degrees out and therefore using it in this state is not reliable.”
She has three golden rules:
- Keep your compass away from electronic gadgets you are carrying and hold it well away from your body when using it
- Make sure you take note of contours on a map. If the route under your feet is not what you anticipated, the alarm bells should ring. Stop and re-evaluate
- Always carry a spare compass in case of your main one malfunctioning, getting damaged or loss.
More information is on the safety pages of the Mountaineering Council of Scotland website.