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Discussion: different compasses depending on latitude?

in: Orienteering; General

Apr 7, 2012 11:49 PM # 
I was reading a fysic-book about magnetic fieldes in school the other day... a, in generall boring, clase but an article about compasses got me thinking... the article said that the force of the magnetic fieled gets more directed vertically as you move towards the magnetic/geografic poles and therefore you need a counterweight in the north/south-end of the compass-needle so the needle wont get stuck or slowed down becouse it's not horisontal. So the question, though it is unlikely, do orienteerers estimate these kind of circumstances when the comnpasses is made? and do orienteerers in that case change compass when they are passing the equator?
if not: should they? or is it a too weak force to make a difference? --> no matter how hi-tec and sensetive the compasses gets?
Apr 8, 2012 12:03 AM # 
Yes, compasses are manufactured for a specific region, and the counterweighting varies. Manufacturers make up to five versions, though for some of those, there isn't much orienteering in the region. The one that works for Europe also works for North America, and Australia/New Zealand is the other popular one. If you're off by one region, it might not make a big difference, but a compass made for Sweden may not work well at all in New Zealand.

Silva's zones are here:

Some additional information:
Apr 8, 2012 12:11 AM # 
The short answer is yes. Different compasses are available depending if they are going to be used in the northern or southern hemisphere.

I have an older Silva base plate compass that says MN on the back. You;d think that was for "magnetic north" but it is actually for "middle north" meaning it is for the middle part of the northern hemisphere. When I was orienteering in Australia, I had a southern hemisphere compass that said MS on the back "middle south" meaning it was for the middle part of the southern hemisphere.

With that said, my southern hemisphere compass seems to work reasonably well here in the northern hemisphere and I have a friend that oreinteered for several years in Australia without knowing there was a different compass for that region and he used his northern hemisphere compass. Basically the difference is that the needle is weighted so that it lays flat when held perpendicular to gravity in the proper region and if you use the wrong compass, the needle will just appear tilted down (or up)---but it still works.
Apr 8, 2012 6:08 AM # 
My rogaine teammate in the 2009 Australian champs brought her northern hemisphere compass with her (or bought it here, I forget which) and it didn't work at all well. It kept getting stuck so we ended up not going where we wanted to. Mind you, that also happened when I was navigating.
Apr 8, 2012 10:48 AM # 
Its worse than just a needle tilt for low-inertia compasses such as the Silva Jet. A MN needle taken to the MS zone will go crazy when the compass is not quite level. Haven't worked it out but I imagine that its something to do with where the mass of the needle is - very close to the pivot.
Apr 8, 2012 3:07 PM # 
I did the opposite of gruver's situation. I bought a compass from Australia off ebay without thinking about the graphic that J-J posted. It would point north if it were completely level, but it would deflect to the side with very small amounts of tilt.

There are global compasses. Suunto has several. Here's the "orienteering" model.
Apr 10, 2012 4:43 AM # 
"Orienteering" ha ha. Most orienteers are using thumb compasses, Suunto used to produce a thumbie with the global needle but not any more (AFAIK) and I don't know of any others. The needle is reasonably good but not quite as good as the Silva Jet, perhaps because of the little gimbals that cope with the vertical pull of the earth's magnetism. (NB I'm using the word Silva as understood in most of the world, there may be a peculiarity in North America.)
Apr 10, 2012 2:11 PM # 
Do Moscompass mark their models with some kind of region code?
Apr 10, 2012 3:37 PM # 
I have two Model 3s here. One has what looks like "D6" handwritten on the underside of the needle. The other has what looks like "5 D4" handwritten on the underside of the bezel. On both compasses there is what looks like a counterweight attached to the underside of the needle. They are at different distances from the pivot, and on one the counterweight is on the north end, the other it's on the south end. Both compasses work fine in the USA.
Apr 11, 2012 1:45 AM # 
I have a Model 8 here supplied for use in Australia/NZ. On the underside of the needle it says "AU" in what looks like handwriting!

Silva compasses supplied for use in Australia/NZ have "MS" on the packaging but mine has "M A" stamped on the bottom of the capsule.

Various sources talk about 5 zones delineated by the compass industry, using numbers 1-5. Guess its asking too much that they all use the same nomenclature:-((
Apr 12, 2012 12:38 AM # 
My Australian compass worked fine in Uruguay and Brazil. My North American compass (which was likely made in, and balanced for Europe), did not. I believe it was a Silva Jet 5S, or 6, or something like that.

Those from North America and Europe planning to attend WMOC in Brazil in 2014 should plan on obtaining a Southern Hemisphere compass. Like I said, those made for Australia should work fine.
Apr 12, 2012 2:07 PM # 
The US Junior Team has a set of 11 Southern Hemisphere compasses, donated very generously by Gale Teschendorf and GO Orienteering from when the JWOC team traveled to Australia. These compasses are in a sort of lending library and can be borrowed for races in the southern hemisphere.

I don't really know who has the library right now, but I could probably track it down. If anyone is interested, send me an email and I'll try to set it up.

In the past, we have encouraged a small donation to the junior team for using the library.
Apr 13, 2012 7:45 AM # 
First I've heard of this...
Who has them?
Apr 13, 2012 10:22 AM # 
Come on down! Lots of good events and maps here.
Sep 16, 2014 12:41 AM # 
Just adding a comment here to bring this (old) thread to the AP homepage for the benefit of those going to WMOC Brazil.
Sep 16, 2014 6:05 AM # 
Still not sure where the junior team library is just now, but I think they are still somewhere in New England. Would be good to track them down and advertise them properly.
Sep 17, 2014 4:46 PM # 
The junior team library of Southern Hemisphere compasses is in capable hands once more. For now, email me if you have an interest in borrowing such a compass and I'll try to arrange things. This might be of special note to those going to Brazil or to Tasmania for the big upcoming races.
Sep 23, 2015 12:16 AM # 
Does anyone have experience using a compass designed for Brazil or South Africa in Australia? It looks to me from the map above that these would be one zone away. So I suspect it will work, but I would like to confirm before going Down Under.
Sep 23, 2015 12:26 AM # 
One zone away should be fine, even two is reasonably OK. I certainly had no problems using my Australian compass in Brazil so the reverse should also work OK.
May 8, 2016 7:02 PM # 
I'm going to the World Rogaining Champs in Australia this summer and was wondering if those Southern Hemisphere compasses the juniors used in 2007 are still available to borrow/rent. There are others looking to borrow/rent as well. Please let us know if this is possible and how to go about doing it. Thanks!
May 8, 2016 7:15 PM # 
I think that barb bryant might be the right person to contact these days.

Good luck for the rogaine!
May 8, 2016 7:33 PM # 
Thanks, Ross!
May 9, 2016 1:51 PM # 
I'll be heading north for the winter so we can trade if you like. Given we're both in WA it should be an easy trade.
May 10, 2016 1:29 AM # 

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