Contents: Backups

Paper map and compass
– Lost on Scafell Pike

Extra GNSS receivers
Reverse polarized compasses

Electronic compasses
– The magnetometer
– Calibrating the compass
– Electronic vs magnetic compass

Barometers and altimeters
– The barometer sensor
– Calibrating a barometric altimeter
– Effects of height and weather
– Choosing an altimeter app
– Engulfed by mist in the Alps

Paper map and compass

You can’t have too many navigation backups, but however many navigation aids you’re taking, make sure one is a paper map with a baseplate magnetic compass like the Silva Expedition 4. Electronics can fail in a gazillion ways and a nearby military exercise could jam all the working GNSS devices you have.

A map and compass weigh little and never run out of battery. They aren’t bombproof but they are very, very reliable. Put a paper map in a transparent waterproof case. Ortlieb make a great roll top map case that will protect a paper map from the worst weather.

Drop a phone or GPS handheld and a bad landing could kill it. A flat battery, moisture, a fault or a software update could all spoil your day. You might just accidentally leave your phone on, in your pocket. The military might be jamming GPS signals. There are too many ways for electronics to fail.

I also want to highlight the dangers of freezing winter conditions. The ‘remaining battery’ indication can’t be relied on in winter. When it’s very cold, the batteries in electronic devices can fail shockingly early and unpredictably. You can still use electronics to navigate in winter and they might last the day without a problem, particularly if you use lithium-based batteries. However, you must be prepared for them to fail at any time.

If you’re left high on a mountain in bad visibility, without any navigation aids at all, finding a safe way down can be impossible. If you do head out with an electronic navigation device and no backup, then don’t go anywhere where good navigation is important for your safety.

Lost on Scafell Pike

Before GPS handhelds were available there was a time when I was young and not very sensible. I was doing the national three peaks with my brother and his friend. Snowdon, Scafell Pike and Ben Nevis, one after the other. We were planning to start early on Snowdon and go via the scrambly knife-edge ridge of Crib Goch for extra fun. Then off to the Lake District to do Scafell Pike before dark, followed by a drive through the night to start up Ben Nevis before dawn. It would get light as we got higher on ‘The Ben’ and we would finish on the highest mountain in Britain. That was the plan.

We got off to a bad start. My brothers friend who was normally up for most things didn’t like the exposure on Crib Goch and we slowed to a crawl. It takes forever to do 1.5 km of rocky ridge using a bum shuffle.

We got to the end eventually and bagged Snowdon but the big delay meant we didn’t arrive at Wasdale below Scafell Pike until just before dark. The mist was well down on the hills.

Young and poor, we hadn’t wasted any money buying a map for Scafell Pike. I’d done it before and thought we’d be fine, after all, we were going to be doing it in daylight.

None of us wanted to abandon our effort and we did have torches.  So, as night arrived we replaced map and compass with youthful enthusiasm and headed towards Mickledore. It’s a high saddle near the summit which is flanked on both sides by steep cliffs.

Even if we did lose the path, the cliffs should funnel us to the saddle where turning left and heading uphill should take us to the top.  We were slow in the mist but made the top of Scafell Pike OK.  Now we headed down away from the cliffs for an easier path to the valley. We were careful to keep spotting cairns in the gloom to stop us going astray.  It was pitch black and we could probably only see 25m with our torchlight bouncing back off the thick mist.  The cairns petered out. 

We retraced our steps and tried some other lines. We couldn’t find any more cairns and there was no obvious sign of a path over the rocky ground. So, we tried to maintain the same downward direction as the line of cairns, hoping to pick more up. We never did. We were lost. We kept going down but the ground got steeper and rockier until further downward progress would have needed some dangerous moves. There was no sign of easier ground below.  We climbed back up to try different directions.  Without a map or compass it was hard to guage which direction we were going. Time passed. We thought we’d tried every possible direction but everywhere we went we’d get into steep dangerous ground that we had to retreat from.

With all the standing around, discussing options, we were getting cold and the atmosphere was turning mutinous. My brother was coldest and ready to storm off on his own and take his chances. He needed more physical activity to get warm. His plan was to climb back up and head towards the Hardknott Pass just to try something different. That is a long and complicated walk out, even if you know what you’re doing. My brother had little experience of being in the mountains. To take a chance, without a map or compass, at night , in the mist and alone? At least I knew that wasn’t a good idea.  I persuaded him to hang on by suggesting that we walk back and fore to stay warm until dawn arrived. 

That’s what we did. It was an anxious night. When the light improved, we could see the lie of the land better and found a line down without too much trouble. We came down near the base of Great Gable and I guess we had got stuck somewhere in the tricky ground east of Piers Gill, but I’ll never know. That was about 2.5km from the more direct Brown Tongue route we’d been hoping to walk down.

I’m a slow learner and on another trip, to Snowdonia, half-way round a planned gentle tour of Lyn Idwal we were tempted higher by a mist-shrouded rocky ridge. We had no map or compass. Enjoying ourselves, we kept climbing to the top of the Glyders about 1000m up. We knew we only had to turn right and head down to the top of Devils Kitchen. There we would find a big path back down to Ogwen where our walk began. Cleverly, we noted where the sky was lightest and where the prevailing wind was coming from, to keep ourselves oriented. 

It was a long way down before we dropped below the clouds. Instead of our path to Ogwen we were looking at Pen-y-pass and Llanberis not that far below. Despite our best efforts we’d been walking 180 degrees in the wrong direction. We did at least make one good decision and continued our descent. We hitched the 10 miles back round to Ogwen.

It’s not a coincidence that the only two times I’ve been properly lost on mist-shrouded mountains were the two times I was without a map and compass.

For as long as I can remember mountain professionals have advised carrying a map and compass accompanied by the caveat “and know how to use them”. These are the most reliable navigation aids. Some mountain rescues have been successful by coaching the lost party over the phone how to use their map and compass properly. Even if your traditional navigation skills are poor, carrying a map and compass should be an easy decision to make.

Learn how to use them and take a map and compass with you.

Extra GNSS receivers

So, you’ve got a GPS and a paper map and compass. Do you need any other navigation aids? Honestly, how good is your navigation with a map and compass? How confident are you that if your GPS failed you’d be fine on a mist-shrouded mountain plateau, possibly covered in snow and surrounded by cliffs?

A recent post on a popular hiking forum asked if anyone else had come down the wrong side of their chosen mountain for the day. It was a long thread with many people cheerfully sharing their navigation errors. Most carried a map and compass. Mountain rescue reports show that quite a few of us get lost, even though we’re carrying maps and compasses.

It’s much harder to navigate accurately with a map and compass than it is using a GPS. If you go wrong it can be hard to work out where you are. If your own mappy-compass skills aren’t good or you don’t have much experience of navigating in bad conditions, then you would likely benefit from a navigation course.

If you intend to go into the hills anyway, before brushing up those skills, then why not take a second GPS device as well as a paper map.  If you’re with friends, that’s simple, anyone else in the group could arm their smartphone with a free app and map. eg Mapy.cz.

If you’re alone, then a cheap sim-free Android phone would make a good extra navigation device. eg A Motorola Moto E7i Power costs £80 new and has a big 5000mAh battery. That’s many hours of navigating. It contains a multi-GNSS chip that processes signals from the American GPS, Glonass and Galileo satellite constellations. An older second hand unit like the Garmin eTrex 20x would do the job too.

Any spare smartphone should be weatherproofed, charged and kept switched off, or on standby. So if you end up needing it, you’ll be glad to see plenty on the battery indicator.

It is impossible to be lost if you know exactly where you are.

If all your GPS devices fail then you’ve still got the map and compass to fall back on. Even if you can never remember how to take a bearing, just knowing roughly which direction to walk can make a big difference to your chances of getting down safely. If you don’t know how to use your map and compass and you do adventurous walks, then you should learn. You are very vulnerable without those skills.

Reverse polarized compasses

Until handheld GPS technology arrived, a map and compass were what a mountain hiker carried for navigation. There are still old-school types confidently asserting that you’re better off with a map and compass under all circumstances and that you should leave your GPS behind.  I think they are very obviously wrong. If you carry both a GPS device and map/compass (and know how to use them) then you are better equipped and less likely to get lost than someone who only has a map and compass.

If you lose your grip on a wind-blown map and see it fly off a misty precipice or break your only compass, it’s obvious you’re in trouble. However, you might not be aware that you have a problem if your compass has reversed polarity.

Many bits of modern tech have magnets in them and if your compass sits too close to one it can become magnetised the wrong way. The north end of the needle may even point roughly south.

I had a chat with Heather Morning. She was the mountain safety officer for Mountaineering Scotland when we spoke. She spent 17 years with the Cairngorm mountain rescue team and has a lot of practical experience with compasses. I was interested to learn how much of a problem this was.

She explained that over 20 years ago she would have been quite confident that a compass was a reliable instrument. She couldn’t say that in 2021. She would sometimes have 24 students on a weekend navigation course. All were loaned a good quality Silva baseplate compass. It wasn’t rare for two compasses to reverse polarity over the weekend. Intermittently Heather would send a clutch of compasses back to Silva to be re-magnetised.

“Magnetic fields exist around items such as mobiles and smart phones, magnets hidden inside mobile phone cases, avalanche transceivers, radios, personal locator beacons, GPS, cameras, car keys and even small magnets on belt fastenings, not to mention the tabloid favourite – under-wired bras.

Some outdoor clothing and equipment manufacturers have started using magnetic fastenings instead of Velcro or zips – on jackets, rucksacks and even on gloves, and these can have a major effect on a compass needle.

Other things which can affect a compass before you even reach the hill include security loops as you enter outdoor and food stores or speakers in your car doors or on parcel shelves.“

Mountaineering Scotland

If you remember, you should check your compass is working as you start your walk. If you don’t do that and you’re mid-walk when the mist comes down, be careful if your compass behaves oddly. Maybe it’s been affected? Is the terrain what you were expecting?

“The compass needle may just be very briefly, partially or totally reversed when in close proximity to any of the items mentioned above. If the needle becomes sluggish and slow to settle (it may appear to stick and be out of balance) it has become partially reversed. If the ‘north’ arrow (usually red) is pointing to south instead of north, then your compass has become completely reversed”.

Mountaineering Scotland

Make sure compasses are carried away from any magnets or electronics and don’t pop any into the same pocket as your phone. Smartphones contain a surprising number of magnets. The loudspeakers may have several. The autofocus motor on the camera lens, the microphone and the vibration motor that makes your phone buzz, all contain magnets.

When you get home, store compasses somewhere magnet-free and don’t put them on your loudspeakers. They contain large, powerful magnets.

I’ve always been aware that magnets are a threat to compasses and have stored mine reasonably carefully. I’m more likely to ditch compasses because of air bubbles forming inside them.  I‘ve never had any polarizing issues. If you keep them away from magnets they should last for many years.

However, if the mist comes down whilst you’re on featureless ground and you have an affected compass, you might not discover you’re going the wrong way until you reach an unexpected feature. At that point it might not be obvious where you are and without another means of navigation you could have a difficult day.

A smartphone or other GNSS device can pinpoint precisely where you are in a few seconds. Even if you’re a traditionalist who swears by a map and compass, your life is not made harder by being able to learn exactly where you are. To guard against the reverse-polarized compass, take a spare compass and put a nav app and offline map on your phone.

It’s impossible to be lost if you know exactly where you are.

Electronic compasses

The magnetometer

Imagine…your GPS units have all been ‘jammed’ by the nearby military exercise and you’ve just broken your favourite compass. If there’s no spare compass, you might think about using the one on your smartphone or other GPS device.

Phones, GPS handhelds and watches are rarely used perfectly flat and demand a different solution to a magnetic compass. The sensor at the heart of an electronic compass is called a magnetometer. It has 3 sensors at 90 degrees to each other. They can sense how strong the magnetic field is along each axis and will work with the device at different angles. However, the three magnetometer sensors will provide quite different readings depending on what angle the user holds the device. More information is required to learn where north is.

Accelerometers and gyroscopes in a phone determine what angle the device is at and how quickly it’s being rotated. Combining information from the accelerometers and gyroscopes with the magnetometer data allows a phone to work out the strength of the magnetic field in every direction.

That still isn’t enough to know where true north is. The phone must also know what the earths’ magnetic field is doing at it’s location. It varies significantly at different places on the planet and changes year on year. The ‘magnetic declination’ is shown on all OS maps and must be allowed for when using a traditional compass. It must also be allowed for by the electronic compass.

As I write, the magnetic declination on the west coast of Skye, UK is about minus 3 degrees, at Lowestoft, UK it’s about + 1 degree. A difference of 4 degrees. In Rio de Janeiro it’s a very significant -23 degrees. Those are big variations that must be corrected for if there’s any chance of smartphone maps being properly aligned, or the electronic compass pointing north. (figures from magnetic-declination.com)

The British Geological Survey have a team that maps and models the earths’ magnetic field. This information is made available to companies like Google and Apple who build that model into their phones and keep it updated. Once the phone knows where it is, it can reference the BGS supplied model to know what the earth’s magnetic field should be doing there.

Combining information from the magnetometer, accelerometers, gyroscopes with knowledge of the earth’s magnetic field allows the phone to show where true north is. Clever stuff.

Google maps, offline maps and anything else that uses the electronic compass will align with true north not magnetic north. This is an important point, you should expect a smartphone’s electronic compass to point to true north everywhere, including in Rio de Janeiro. This could be quite different to where a traditional magnetic compass would point.

If you do ever use an electronic compass, you do not have to allow for magnetic declination as you would with a magnetic needle compass. The electronic compass will probably point to true north. For maximum accuracy when map reading with an electronic compass, you should allow for the difference between true north and grid north instead.

Qn: Which North does OS Locate use?

Ans: OS Locate points to True North (towards the geographic North Pole). True North is different from Grid North in Britain by up to 6° (but they are the same along the line of longitude 2° West). If you require accurate compass bearings, we do not recommend using the phone’s internal compass, but instead use a dedicated compass.

Ordnance Survey FAQs

Although an electronic compass is very clever, the Ordnance Survey explain that smartphone electronic compasses are not very accurate. That’s been my experience too. To quote the OS Locate app’s FAQ again.

Qn: How accurate are the compass features in OS Locate?

Ans: “In our tests with various devices, they are mostly accurate to within a few degrees, once calibrated. Unlike traditional compasses, your phone compass will need regular calibration – usually each day or two.”

Ordnance Survey FAQs

Calibrating the compass

The trouble is, no matter how thorough you are calibrating a magnetometer compass, you can’t know for sure how accurate it is. You could compare it to a magnetic compass, but if you’ve got one of those you don’t need the magnetometer-based compass.

However, in an emergency, the electronic compass should be much better than nothing and you don’t have to allow for magnetic declination as you do with a traditional compass.

An electronic compass can be badly affected by external magnetic fields just like a magnetic compass. So, keep it away from magnets and calibrate it before use. Then it might even be reasonably accurate.

It’s worth knowing how to calibrate your phones compass. Then if you do use it, it will be as accurate as it can be. It involves moving the phone through all three planes, to calibrate the magnetometer. Holding it in your hand and describing the figure of 8 shape as shown below forces it to do that.

– – – – – – – – – –

Android 11: Calibrating the compass

• Open the Google Maps app.
• Tap the centre button to put the location icon centre screen.
• Tap the location icon.
• Tap the ‘Calibrate’ button. Accuracy is described as Low, Medium or High.
• Move the phone through three figure of eights as described by the phone. Obviously, you’re aiming to get accuracy ‘High’.
• Tap ‘Done’ to finish. 
• The semi-transparent blue fan that indicates in which direction you’re pointing the phone gives an indication of the compass accuracy. The larger the angle covered by the fan, the less well calibrated it is.

My experiences with my Android phone aren’t encouraging. Sometimes everything seems fine and the electronic compass seems to be working OK. At other times with different apps I get odd results with the direction shown being a long way off. I’ve had the location arrow on OS Maps point in random directions whilst using it. I don’t trust the electronic compass and would only use it if I’d run out of other options.

– – – – – – – – – –

iOS 14: Calibrating the compass

• Settings > Privacy > Location Services > System Services > Compass calibration – check it’s switched on.

If the switch is on, then the iPhone will try to keep the electronic compass calibrated automatically. Despite my iPhone getting regular use, when compared to my magnetic compass OS Locate showed an 11-degree error. I did a few figures of 8s with the iPhone, then it matched the magnetic compass more closely.

The iPhone X has been better than the Samsung S10e but the automatic compass calibration doesn’t seem to work. If you’re ever forced to use it, do some figure 8s to calibrate it and keep your fingers crossed that does a good job.

Electronic vs magnetic compass

I’m very happy navigating with GNSS technology but I’ve little faith in a smartphone’s electronic compass. A baseplate magnetic needle compass is much better. Polarizing disasters aside, it will always point to magnetic north and be a more reliable tool for judging direction. No calibration or battery necessary.

Silva claim an accuracy of 1 degree for their compasses. If you can navigate with one-degree accuracy, then give yourself a pat on the back. After a kilometre of walking, the farthest off course you’d be is 17.5 metres. Very good. A GPS device will normally do better than that, over any distance, whether it’s 1km, 100km or 1000km.

Take a traditional compass and only resort to the electronic compass if you’ve no better option.

Barometers and altimeters

The barometer sensor

Most smartphones have a barometric sensor. GPS watches and handhelds sometimes do too. This sensor measures air pressure. Air pressure reduces predictably with height. So, a simple app can convert a phone to a good altimeter. An altimeter is a very useful nav tool as it can identify which contour you’re on.

A good barometric sensor is so sensitive that it can tell the difference between the device being held by your feet or by your head. It works completely independently of anything else so can be used as a standalone device in the middle of nowhere. It doesn’t strain the battery on a phone or other device.

Calibrating a barometric altimeter

We all know from seeing large wall-mounted barometers that the air pressure changes with the weather. If a barometric altimeter gives an elevation for any given location on Monday it might show something totally different for the same spot on Wednesday. It could be so far off to be completely useless.

You can’t just start up a barometric altimeter app and expect it to provide a useful reading, it’s likely to be miles out. However, if the altimeter is regularly calibrated it’s a surprisingly accurate tool and calibration is easy.

The air pressure over a few hours doesn’t normally change hugely. So, whenever you’re hiking and reach any distinctive feature like a mountain top, a saddle on the ridge, a river crossing, a tarn or path junction you can get the elevation from an accurate map eg An OS map. Entering that into the altimeter calibrates it accurately and will ensure that for the next few hours it will be a useful guide to height. If conditions get difficult, knowing which contour you’re on might be very useful information.

If little time has elapsed since calibrating the altimeter, it could be more accurate than a GPS-derived elevation. The GPS vertical error might be three times the size of the horizontal error. That could be ± 45m with a very old GPS receiver. In my limited experience a recently calibrated barometric altimeter should be good for ± 10m.

A barometric altimeter won’t stay properly calibrated for very long. A few hours ‘ish. It’s useful to understand how much the changing weather affects the accuracy of the altimeter over the course of a day. If the weather’s changing fast, it could make a significant difference.

Effects of height and weather

The pressure at sea level is often quoted with weather forecasts, usually in millibars (mbar) although the units sometimes get shown as hectopascals (hPa). Millibars and hectopascals are the same.
900 mbar = 900 hPa.

The higher you climb, the less air is above you and the lower the pressure gets. At lower elevations (approx up to 4000m), for every 10m of height you gain, the air pressure will drop roughly 1 mbar. That’s a good rule-of-thumb for all the mountains in the UK. The barometer sensor measures the pressure drop accurately as you climb but that accuracy will be spoilt if the atmospheric pressure changes significantly.

Settled weather is generally accompanied by high pressure. It generates those blue sky, hazy days in summer and the still frosty days in winter. These high-pressure weather systems tend to move slowly and the pressure might only vary by 2 mbar over the day. However, if a big low-pressure system is moving in fast off the Atlantic, with strong winds and rain, then the atmospheric pressure might drop a mbar every hour. If the pressure in the centre of a powerful low-pressure system drops by 24 mbar over the course of 24 hours, meteorologists refer to it as a ‘weather bomb’. Expect bad weather!

For every mbar the atmospheric pressure drops, the altimeter will show your elevation 10m higher than it should, just as if you’d climbed up 10m. If you calibrate the altimeter at 10 am as a ‘weather bomb’ is approaching then by 6 pm, without any extra calibration, it might over-read by 80m. Conversely, if the atmospheric pressure is rising the altimeter will tend to under-read as the day progresses.

Significant changes in air temperature affect the accuracy too. The bottom line is that the more often you calibrate your barometric altimeter, the better. Even with an approaching ‘weather bomb’, if you can calibrate a barometric altimeter frequently it will still be a helpful tool.

If you get a weather forecast then note how the pressure is expected to change over the day. That will help guage whether a barometric altimeter will under or over-read as the day progresses. It can also inform your decision on how often to calibrate it.

XCWeather.co.uk forecasts show the local sea level pressure every hour throughout the day, for any location across the UK and a few countries in mainland Europe too. Average pressure at sea level is around 1013 mBar. 980mBar is a very low pressure and 1040mBar is very high (at sea level).

Choosing an altimeter app

A very simple app will do the job. It must display elevation based solely on the barometer sensor and you must be able to calibrate it by manually entering the correct elevation. Apps that offer this are surprisingly hard to find. Many altimeter apps get elevation from the GPS. However, if your GPS receiver is still working you don’t need any help from an altimeter because you’ll already see your position on a map.

A GPS-derived elevation should always be roughly right (particularly from a better dual-band unit) but a manually-calibrated barometric altimeter can do a good job without any GPS help.

Here are a couple of apps that do that. You can deny access to the GPS receiver for both apps to avoid wasting battery. Both will happily work with the pressure sensor alone.

Android App: Altimeter Plus.
Developer: PlainTap.
The elevation is provided in big numbers on the screen along with a ‘Calibrate Sensor’ button. Perfect. There are two small central buttons. One selects units (metres or feet) and the other allows the app to get the elevation from the GPS instead. However, if your GPS is working you won’t need this, you’ll already know exactly where you are.

The ‘Sensor Calibration’ screen even comes with a reminder of how the barometric altimeter works and the importance of regular calibration.

iOS app: Barometric Altimeter.
Developer: Stephan Haeuslschmid
Another simple app that displays the altitude and offers manual calibration.

Engulfed by mist in the Alps

Many years ago a friend and I planned to climb a few mountains in the Swiss Alps, around the big glaciers that form on the southern side of the high mountain ridge that includes the Jungfrau, Eiger and Monch. The weather was terrible and we were hanging around in the Finsterarrhorn Hutte at an altitude of 3048m. It was very wet and the sky was covered with a thick blanket of grey cloud. At night the usual freeze wasn’t happening and any lying snow was heavy and soft. On some slopes it made uphill progress almost impossible. 

The Finsteraarhorn ‘hut’ is a huge modern mountain refuge, surrounded by big mountains and glaciers. It can hold over 100 people. The bad weather explained why we were almost the only people there. There was just one other small party. We had all decided to head for the comforts of the valley.

It was about 16km to where we’d left the car at the east end of the Oberaarsee lake around the 2,300m contour. The walk involved negotiating four glaciers and we had to climb over the Oberaarjoch, a low point on a rocky mountain ridge between us and the car. The Oberaarjoch is home to the small Oberaarjoch hutte at 3255m and provides the only easy way across the ridge.

The other party got away in the morning much more promptly than us and headed off down the ice of the Fieschgletscher. An hour or so later we set off. The weather got worse as we descended. After 4km of downhill ice we left the Fieschgletscher to climb back up a more crevassed glacier towards the Studergletscher, which flowed down the valley directly below the Oberarrjoch. It began to rain and the wind increased. The temperature dropped and we soon had hoods and gloves on, zips up tight and heads down. Visibility was awful. It was grim. As time passed we started to get cold and we became anxious about finding our way in the bad conditions.

As the gradient of the ice eased we could see from the map that we needed to take a right turn roughly 1.5km further up the glacier. There we must head up steeper snow slopes to find the Oberaarjoch.

However, we were now engulfed in thick mist. When should we turn right? We couldn’t even see the base of the nearby rocky ridge on our right. It was an impenetrable thick white gloom in every direction. We climbed up the side of the glacier to get closer to the ridge hoping to see something useful but the mist was too thick to see anything more. The slope just made walking harder.

We stumbled across the footprints of the other party. They had obviously decided to do something similar and we saw their track taking a steeper line up towards the ridge. The wrong line could involve 300m of height gain over 1km into the big snowy bay below the nearby Oberaarrotjoch. It was the wrong way and would need reversing if we made that mistake. We had no idea if the other party knew the way, or if like us, they were on unfamiliar territory.

We discussed our options, I had a Suunto watch with a barometric altimeter on it. The poor weather had encouraged me to calibrate it earlier at the hut where we knew the exact height. That meant it should still be quite accurate. I had never used the altimeter in anger before but I had often kept an eye on it and always been impressed at its accuracy. Now we were going to rely on it.

The map showed that we needed to be on the 3060m contour before we turned right. The altimeter showed us nearer 3000m.

That suggested we needed to go another 800m up the gently sloping glacier to the 3060m contour before turning. We walked up the centre of the glacier through the white gloom until the altimeter said 3060m. We stopped. If the altimeter was accurate, we had a good estimate of where we were. We took a bearing from the map on the Oberaarjoch and headed off on that bearing for what we hoped would be the low point on the ridge and the refuge. Conditions were now terrible, strong winds, thick mist, pouring rain and very cold. It was summer in the Alps but conditions were like bad Scottish winter weather.

The best part of a kilometre later, it was with some relief that we saw the Oberaarjoch hutte emerge from the gloom above us. We were bang on course. Hats off to the altimeter. There was so much water running down the rocks above the hut it was like walking through streams to get inside. We hurried into the hut to warm up.

The other party had made it to the hut before us but not without a struggle. One of the group had become hypothermic and wrapped in blankets, was being tended to. They were going to overnight at the hut.

We were very glad to get out of the awful weather. We took our time warming up and refuelled with some food and hot soup. All our layers went on before heading down the Oberaargletscher. With gravity on our side and fewer navigational challenges, the 8km to the car at the far end of the Oberaarsee lake was easier work.

You can’t have too many tools to help position you on the map.