Compass - I can't figure this out!

[Lithril]

Ok I've been using compasses for a while and I understand the principles on how they work (have to teach it to 11-16 year olds...) but I'm stumped at this one.

Usually use Silva compasses as they're basic and fairly robust, we give them to the kids for DoE to use. I went out last weekend and there were 3 compasses in the group, the kids had 2 and I had 1, all identicle and made by silva. I put my compass in my top pocket (nothing else in there), next time I took it out to check a bearing, walked about 200 meters and the compass swithced so that north points almost to south and vica verca. Only happeded with this compass and its still like it, so a permenant change.

Any ideas?

Matt

[Toddy]

I thought that only happened to me
No idea, though my destruction of compasses has been blamed on walking too near to an electricity sub station, passing under pylons, thunderstorm and my rucksack containing the compass being left too near to a fire. I can't see any of them really being responsible but I'd love to know what reason you finally come up with

Cheers,
Mary

[Swede]

It happened to me too. I noticed that the compass showed 180 degrees wrong. For that time i worked in a shop. We had a strong magnet mounted on the desk in the shop to demagnetize the pricetags (prevent shoplifting). By putting the compass on top of the magnet it became "set at zero" and was OK again. I don´t know if a cellular phone or anything else with a strong magnetic field are to be blamed. /Swede

[Roving Rich]

Prolly too close to your pacemaker Lith

Cheers
Rich

[merlin]

magnets can go a bit funny if they have a bang even a small one, maybe a small bang and its lost some strength allowing it to affected by something small you have on you, watch or something else metal??

[oldsoldier]

I think the poles just changed for you!!

[The Joker]

I think the poles just changed for you!!

On some tv prog the other day i was watching they said we're suposed to be nearing a time when the poles swap

[rik_uk3]

Ok I've been using compasses for a while and I understand the principles on how they work (have to teach it to 11-16 year olds...) but I'm stumped at this one.

Usually use Silva compasses as they're basic and fairly robust, we give them to the kids for DoE to use. I went out last weekend and there were 3 compasses in the group, the kids had 2 and I had 1, all identicle and made by silva. I put my compass in my top pocket (nothing else in there), next time I took it out to check a bearing, walked about 200 meters and the compass swithced so that north points almost to south and vica verca. Only happeded with this compass and its still like it, so a permenant change.

Any ideas?

Matt

Saw the same thing in an episode of the X-Files

[Chopper]

You need to re magnetise the needle.

Get a small bar magnet use only the North pole end and place it on the glass dial and then slide it along the glass towards the tip of the north (RED) end of the needle, do this about ten times and it should bring it back to life.

Make sure that you only do it to the red half and not the white half, we used to have a really dopy scout leader and I magnetised the white (South) end of the needle and then gave the compass to him on a hike, it took him about ten minutes to realise that there was something wrong and he never really switched on to the fact that it was a windeup, quite worrying that someone so stupid could be allowed to be responsible for our kids.

[Rod]

Hi Lith,

You can send the compass back to Silva and they will realign it for you - also will take bubbles out of the capsule. Take it in to your local Cotswold and get them to send it off for you.

[gregorach]

I've had the same thing happen to me. Darned if I could figure out what had caused it...

[Lithril]

Hi Lith,

You can send the compass back to Silva and they will realign it for you - also will take bubbles out of the capsule. Take it in to your local Cotswold and get them to send it off for you.

Fantastic, cheers Rod, I didn't realise they would do that, I was going to bin it.



Thanks for the responses.

Matt

[Chopper]

Fantastic, cheers Rod, I didn't realise they would do that, I was going to bin it.



Thanks for the responses.

Matt

When i asked Silva direct if they could remove bubbles they said that it could not be done, and why go to the tropuble of returning the compass when you can fix it yourself in two minutes.

[BorderReiver]

Bit worrying this.The accepted wisdom is "always trust your compass".

So if you are in unfamiliar territory and you trust a dodgy compass,you could land up in trouble.

Just as well to carry a GPS as backup.

[anthonyyy]

I can understand exposure to a magnetic field altering the compass and putting it a bit "off" but an 180 degree change is wierd.

[Chance]

Would it have been near a phone ? Or anything else with a speaker in it ?

[FGYT]

Bit worrying this.The accepted wisdom is "always trust your compass".

So if you are in unfamiliar territory and you trust a dodgy compass,you could land up in trouble.

Just as well to carry a GPS as backup.

which is why you should always carry 3

[Glen]

Bit worrying this.The accepted wisdom is "always trust your compass".

So if you are in unfamiliar territory and you trust a dodgy compass,you could land up in trouble.

Always worth checking, with the Sun, to make sure your compass hasn't done a pole swap.

[stuartmac5]

hi Lithril,

a neodymium magnet is amazingly powerful and kids in classrooms can have a bit of a prank, whearabouts they can use one to change a normal classroom bar magnet from n-s into s-n. They are that powerful.
maybe some of the kids with you were taking out that day were having a bit of a prank with you?
did you let that compass out of your grip?

Im obviously a suspicious person

[Voivode]

And on the topic of neodymium magnets, I use a 10mm diameter disc magnet to realign my compasses when they spend too much time close to emf sources, like the wiring in the walls, televisions and such. I found in my apartment that over time my compasses (I have 2) would gradually become demagnetized and just spin freely. A single application of the rare earth magnet pops them right back into shape.

I don't see why your compass would fail in such a manner, as it requires a magnetic field to realign the field of the pointer. There must have been an outside source that influenced your unit...

[Emma]

Bit worrying this.The accepted wisdom is "always trust your compass".

So if you are in unfamiliar territory and you trust a dodgy compass,you could land up in trouble.

If you're in unfamiliar territory and you don't trust a dodgy compass, you could land up in trouble.

[Lithril]

If you're in unfamiliar territory and you don't trust a dodgy compass, you could land up in trouble.

I've normally at least one other compass but normally I wouldn't use it for micro nav just as a check, only in the New Forest so the compass on my watch was more than accurate enough to check the route that the kids were taking (they also had their own compasses).

It has made me rethink my kit list slightly though and plan to carry a spare.

[PhilParry]

So what you're not saying is that you walked in the wrong direction for a whole day?!?

Ok I've been using compasses for a while and I understand the principles on how they work (have to teach it to 11-16 year olds...) but I'm stumped at this one.

Usually use Silva compasses as they're basic and fairly robust, we give them to the kids for DoE to use. I went out last weekend and there were 3 compasses in the group, the kids had 2 and I had 1, all identicle and made by silva. I put my compass in my top pocket (nothing else in there), next time I took it out to check a bearing, walked about 200 meters and the compass swithced so that north points almost to south and vica verca. Only happeded with this compass and its still like it, so a permenant change.

Any ideas?

Matt

[quarterstaff]

I have a small marbles compass and at first it was ok,then one day I used it just to check my direction and it was way off,mate had his gps,bit miffed,tried a few days later spot on again,next time way off,it was then that I realized that I had got a new copper arthritis braclet with magnets in and I had been using the compass in the left hand-ok,right hand-way-off .
cheers

[Pete E]

I had the same 180 degree swap happen on a Silva Type 27 last year..No idea what caused it as I am careful to store my compasses away from any magnets or stong electrical fields...

Anybody any suggestions as to the best way to store a compass to prevent this happening???

[Voivode]

A box made from a ferromagnetic material (iron, steel, whatever) will create a Faraday Cage effect and shield the object contained within from external magnetic fields; Your compass won't work inside the box, but it should be immune to demagnetization.

[Pete E]

A box made from a ferromagnetic material (iron, steel, whatever) will create a Faraday Cage effect and shield the object contained within from external magnetic fields; Your compass won't work inside the box, but it should be immune to demagnetization.

Voivode,

I wondered about the same idea... I agree that such a "cage" would isolate the needle from the effects of the earths magnetic field, or anyother external source,but storing a magnetic needle that close to a ferro substance, even if it does surround it, surely can't be good??

Regards,

Pete

[demographic]

A box made from a ferromagnetic material (iron, steel, whatever) will create a Faraday Cage effect and shield the object contained within from external magnetic fields; Your compass won't work inside the box, but it should be immune to demagnetization.

A Faraday cage doesn't have to be made from a ferromagnetic material as the MRI room at the local hospitals farraday cage made from copper sheet.