UKC

Just experienced this for first time. Nearly turned back in confusion. Its 2 compasses from now on.

Any ideas as to how the compass got into this condition? I usually carry two compasses but rarely use them (not big on walking without views these days).

I'm convinced one of mine did this mid way through a mountain marathon resulting in me being 180 degrees out, then it switched back, although to be fair it could have been the zero vis and me forcing the map to fit the ground that was the issue...

This happened to me a couple of years back on the Trotternish Ridge.  It was fine on day 1, and then reversed on day 2.  Of course, you can handrail the ridge for most of the way, but there was one section where I passed through a little col system in poor vis which took me an age - you would think it would be fairly easy to get your head round navigating "backwards" but it's surprisingly tricky!

In my case, the weather was terrible when I put my tent up for the night and I chucked stuff in quickly without thinking too much. I had my compass in the pocket of one jacket and my phone in the pocket of another. I hadn't worn them together, but I suspect they came into conjunction somewhere in the unitdy heap of clothes in the tent...

Leaving it beside a speaker, TV etc can do the trick.

You can measure magnetism using a number of smartphone apps...

https://www.kjmagnetics.com/blog.asp?p=iphone-fun

If you have two how do you know which is wrong?  The minimum number of devices needed to detect a single incorrect reading is 3.

I borked a couple of compasses with my mobile phone - my guess was the NFC feature, I keep them apart now.

3 is correct provided you don't have any other information but clearly here they did (map, history, sun, sense of direction etc etc).

Experienced this with my Silva 4 360 in the Lakes earlier this year.* I put it in the top of my bag and for a short time it was next to my phone. My phone was in a wrap-around case with a magnetic latch which probably interfered with it. 

It's quite easy to fix. I got home and swiped the south pole of the same magnetic latch along the compass' north needle, from the centre and quite quickly. After several swipes, the needle flicked sharply back around to its original position. I've tested this with other compasses and it's as accurate as it should be. 

*Fortunately, we soon realised the bearing was the wrong way round and made our way down from Red Screes all fine

Magnet in speaker, vibrator or just the electrical current. The mobile phone problem long predates NFC, which, being utterly tiny power, is an unlikely suspect.

Easy to test if your phone is a threat; bring the compass towards it. If the needle starts to move, it's a threat.

not if all three have been affected by some phenomenon or other.

A compass should be checked against a datum regularly and arguably before it is usedin nearnest  in the absence of any reference point

I have only experienced this once and fortunately it was at home.   I have seen another party confused by a reversed compass and struggling to get their "bearings" coming out of Ennerdale towards the Great Gable area.

warnings should have been given when the government made some of our coins of ferrous metal !

By setting the map using the compass in good visibility.  Hopefully it will be clear that using one compass aligns the map with the landscape correctly (depending on local magnetic variation) while the other does not.

Indeed; but then if you’ve diagnosed the problem from other factors you don’t need another compass, you just need to use the first one backwards.

As in my previous post though, when I had to do this in anger, it was surprisingly confusing for something that seems conceptually simple.

What, using the non red end of the needle instead...?

https://www.glenmorelodge.org.uk/reverse-polarity-in-compasses/#:~:text=Rev....

I read this the other day, and confirmed when I placed my compass next to the speaker on my phone. It seemed to right itself shortly after I waved it about near my phone a bit more.

It will be the neodynium magnets in the speaker.  NFC wouldn't do that.

Yes.  However, I was on my own, in the sort of visibility where you can't see the end of your trekking pole, getting cold and not thinking the straightest I ever have. It seems simple, and I imagine it probably is simple under controlled circumstances.  But, when circumstances are not controlled, things that seem like they should be simple aren't always.

Also, note - it was trickier than I thought it should be, but not impossible.  I did, afterall, make it down!

I’ll have to try it.  I could well believe it though given how confused I get with things like pin numbers on connectors swapping through mirror flips.

I just take a book to keep me amused in the tent, but each to their own. 

Check against the 'compass' on your smartphone - it will tell you which is north vs south at least - I thought it relied on the gps but did a quick google and it appears there is some form of electromagnet (based upin the hall effect)

Your phone could use both. 1) an internal compass calibrated by spinning the phone around 2) navigation apps comparing your current position with previous positions and working out your direction of travel. This can confuse people who don't know the difference between (1) and (2).

Thanks all. Clearly a fairly common complaint but a first for me in...ahm.. 50 hill years. Fixed compass with assist from Google search and domestic magnet. Confidence rattled a bit though.