Magnetic Zones & Global Compasses
In my search for a new compass for my big trip I have discovered a fact that I wasn't aware of and maybe worth repeating here because compasses are a critical item of equipment and
a)others might not know about it, or
b)I may be a naieve idiot in need of putting straight.
Basically, it goes like this..
The earth is dived from north to south into a number of magnetic zones or 'slices'. These relate to how much the needle dips toward the magnetic pole. When you buy a normal compass, the needle will be balanced for a particular zone, usually marked on the back as MN (magnetic north), NME (north magnetic equator), ME, SME, MS. If you try to use it in a zone at a largely different latitude, the needle will hit on the case because it will be unbalanced. i.e. Your compass bought in North America will not work in Australia. If anyone can confirm that they have actually experienced this problem it could be enlightening.
There are 'global' compasses on the market that use different patented techniques to enable them to work in all zones.
I was looking for mirror sighting compasses with a clinometer and declination adjustment and I found the Silva Voyager 8040 but I'm not that keen on it because it doesn't have a transparent baseplate (good for working from maps). I also found the Suunto MC-2G and the Recta DS56. These both have transparent baseplates and are my preferred choice. The Recta and the Suunto look very similar and I read that Recta are part of the Suunto group so they might actually be the same compasses marketed under differnet names. Does any compass experts out there know?
Also, has anyone used compasses from Suunto or Recta and can vouch for their quality? I have only ever used Silva and that was a long time ago. They all claim to be 'world leaders', but the proof of the pudding....
Sorry if that was all a bit long winded.
I am not an expert, but I have done quite a bit of land nav in the Army as well as hunting. First of all any cheap compass will give you a correct direction. The diffrence is how fast they get on track. Let me explaine, if you have two compasses, one a cheap piece of crap, and the second the best in the world. Both will point to magnetic north very relibaly. The piece of crap will take longer and the needle will bounce longer than the high dollar one. But in the end both will point the same direction. Silva, sunnatu and brunton all make reliable products, so figure out what works for you, but don't spend too much money, it usually is a waste. As for a global compass it may be cheaper to buy two. One for north of the equator, and one for the south. A thing to remember is the magnetic north is always shifting, so if you are consistantly off one or two degrees from you map it probably isnt you. Unless you are going cross country for thousands of miles this isnt a problem. In fact you error is probably more than the magnetic shift. Remember to ALWAYS compansate for the magnetic vs true north. Also many a person has gotten lost because they didnt believe their compass and headed in the "right" direction. Another quick reminder metal objects like vehicles, power lines, watches etc can throw off your compass. If your life depends on a bering drop everything and step a few feet away to be as accurate a reading as possable. I hope this helps.
The global compasses actually aren't that expensive. It works out cheaper to buy one of them than to buy two zone specific ones, unless of course I went for christmas cracker variety but they don't have declination adjustment (useful so that I don't have to keep doing the maths) and clinometers (useful for improving my chances of winning bets about whether I can get up that hill) the small amount of orienteering I've done in the past was enough to teach me that really cheap ones that take ages to settle are annoying. It's a good point though, theres no need to spend loads. The Suunto one gets it's 'globality' by separating the magnet from the needle (how does that work then?) but the Silva Voyager just has an ME balanced needle and a deeper case. Don't know how the Recta does it.
I'm glad Recta didn't add an 'l', I don't like the sound of a Rectal compass.
Andy, you’re right on the money with your explanation.
I would still buy 2 (or more) compasses as a backup as well as one of those wrist watch compasses. You might loose or break a compass easily. I lost mine in the Sinai Peninsula once in the pre GPS area. Luckily for me the canyon I was driving through didn’t leave room for error until I reached the sea shore. Has it been in the Sahara, I don’t think I would be typing this now http://www.horizonsunlimited.com/ubb/smile.gif.
OasisPhoto.com – Images from the Magical Sahara.
ShortWheelbase.com – Jeep preparations.
Yeah I was planning to have my super duper does everything compass, plus a cheap spare, plus a button compass in a survival kit that only gets opened in an emergency. Three should be enough.....I hope ;-)
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