Gear

I purchased a Silva Expedition 4 compass in Keswick last month, brought it home and stuck it in the cupboard without opening the package. I've now opened it today to get familiar before i use it and it appears the red (N) point of the needle is pointing South and the opposite white end is pointing North!

Has anyone else had this problem? It hasnt been exposed to any magnetic fields i'm aware of. Does anyone know if it can be recalibrated or if Silva have some sort of warranty (i cant find any online). I havent even used it yet!

Don't panic!

It's actually very easy to 're-magnetise' a compass so that it points the wrong way. Something as simple as sliding it across a steel table-top or work-surface can do it. The problem is, the compass needle is nothing more than a weak magnet, so it can easily be affected by any other type of magnetic material. I wonder if the shop in Keswick had a steel work-top? Or maybe the scanner that logged the barcode was surrounded by steel? Or maybe you plonked it on a steel surface in your car... or at home? One way or another, the needle has been re-magnetised the 'wrong' way and it's a problem that manufacturers such as Silva are well aware of (even though it obviously puzzles the poor customer). Simply tell Silva about it, and as far as I know, they'll switch the polarity free of charge. Just remember to keep the compass away from ALL types of magnetic material in future... with the exception of planet Earth... which is just another huge weak magnet! 

Cheers - i've emailed Silva Tech Support.

Thats certainly news to me, if its happened since purchase, it must have been quite innocuous whatever it was. i emptied the cupboard looking for magnets etc! The polarity seems to have completely reversed (North pointer points exactly South etc). I'll see how Silva reply.

I seem to recall that a physical shock such as dropping a magnet on the floor can change it's properties too.

Also electro magnetic fields such as may be found around electical or electronic equipment. In the marine industry electronic equipment has a specified  "Safe distance" from the ships' magnetic compass. Radar magnetrons were the worst culprits with loudspeakers coming a close second. There's been many a skipper whose fitted a cheap car stereo in his wheelhouse has been bemused to find his vessel going off course.

Racking my brain, i cant think of any metal/magnetic objects i exposed it to...except i do have a Sports watch (Suunto Observer) that has compass functionality which has been in its close proximity.

Surely that couldnt have been that the caused the polarity reversal could it? Dont tell me that when i'm map reading on the hills and i have to remember to take my watch off first!

At the risk of sounding daft, have you tried it anywhere else? You're not sitting on a magnetic anomaly are you?

I wouldn't bother racking your brains about HOW it happened, since there are hundreds, if not thousands of ways it could have happened.

There's the old 'how to turn an old rusty nail into a magnet' trick. Take a rusty nail, hold it steady, and tap it a few times with a hammer. Some of the iron molecules will re-align themselves with the Earth's magnetic field. It only needs a small percentage of the molecules to do this, and the rusty nail becomes a weak magnet. Check a sample of tools in your toolbox, because I think you'll be surprised at how many of them are already weak magnets, capable of at least picking up a few iron filings.

Sorry, Chaiman Bill, but compasses in the southern hemisphere still point the same way as compasses in the northern hemisphere. A compass responds to the horizontal component of the magnetic field, and that is oriented (more or less) the same way over the whole Earth. It's only the vertical component that points the opposite way in the two hemisphers, but that's not much use for navigation.

I'm not sure if there is such a thing as a 'southern hemisphere compass', but if there is, it must be that the weight of the needle is distributed differently to compensate for the couple produced on the needle by the oppositley oriented vertical field. On the other hand, I took my ordinary (northern hemisphere) Silva compass to New Zealand, and it worked fine there.

Jim - I was being a little tongue in cheek, but there is indeed a 'southern hemisphere compass'!

You're right about the relative weighting of compasses for north & south hemispheres. If you use a standard Silva in Tasmania for example, it is the south pointing end of the magnetic pointer that gets pulled down. Differential weighting means it would drag. So southern compasses point south rather than north.

Interestingly, there's no need to account for magnetic variation down south; magnetic south is true south.

We had exactly the same problem with one Stu bought. It one possible cause was the demagnetising thing the shops have to deactivate the security strips on the packaging.

We just too ours back to a different branch of Cotswolds and they gave us a refund.

We were very close to either having a domestic about navigation or heading the wrong way off the top of Gable in the mist.I was taking a bearing on my old and tried compass and insisting we had to go one way, he was playing with his new compass and insisting we had to go anotherway. Luckily he gave way ( not like Stu) and  we went the right way. We realised later that the fault was with his new compass, a Silva Ranger, which did not point north or anywhere near that direction.

Footnote:

Thanks everyone for your help, and in particular for the Physics lesson...it sounds like you lot go a bit further a field than my trips to the Lake District and Cheviots..(!).

 I emailed Silva UK as suggested and as Paddy confirmed, they have offered to remagnetise it at no cost if i post it to them.

 I also emailed the shop in Keswick and they have confirmed that if i return it, they will happily post me a new one.

Cheers

Jolly good El Manana!

Here's another thing that people forget about when you get two or more people taking bearings with their compasses. It's very tempting, having taken your bearing, to compare it with the person next to you. Beware - because when you bring two compasses together, if you get them close enough, the magnetic needles will attract each other. Don't laugh if you think it's daft, because I've seen people doing this when they're learning navigation! You need to keep as much space as possible between the compass and any material likely to generate a magnetic field. That means... certain metals... electrical equipment... and OTHER COMPASSES!