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    Re: Re Compass Adjustment - A Cautionary tale
    From: Glendon
    Date: 2005 Jan 30, 14:54 +1100
    Compasses such as your Silva are usually made to operate in one of five zones in the world. However, some compasses have a "global" needle and will operate effectively anywhere in the world. The Suunto and Silva websites have a discussion of the zones, including a global map of the zones. Their websites also indicate which of their products are zoned, or global. I am not aware of any markings on zoned compasses which indicates their zone type, but maybe an email to the manufacturers may settle that.
    In general, I don't think any of the relatively cheap compasses such as yours can be adjusted to work across zones. Some, more expensive or military specification compasses have provision for shifting a weight along the needle to effect adjustment.
    As far as I can tell, marine compasses are also zoned or global. It is unclear to me whether any of them can be adjusted for zone as part of the "compass adjustment" procedure.
    There has been discussion on this list in the past on compass zones. And on groups such as rec.boats.cruising or aus.bushwalking (see the faq for the latter).
    A couple of personal experiences: my 45 year old Silva Ranger TD has proved to be global; a few years back I bought a pair of binoculars from the US which included a compass, didn't give a thought to zones, needless to say the compass does not work here in Australia.
    Lee Martin
    ----- Original Message -----
    Sent: Sunday, January 30, 2005 2:03 PM
    Subject: Re Compass Adjustment - A Cautionary tale

    I recently visited Whistler in British Columbia to experience backcountry skiing. With me I took a Silva “Ranger” Baseplate compass that has served me well for about 15 years and had proved rugged and reliable in some of the most remote parts of Australia. I would, and have, staked my life on it.


    To my horror as we were about to leave Whistler on our skiing trip I pulled out the compass to orient myself and the map and found it would not work. The magnetised end of the needle pointed downwards and would not swing. To get the needle to swing I had to hold the compass at about 45d to the vertical and then the needle would move freely but it was hard to determine an accurate bearing and impossible to use the compass sighting mechanism.


    Obviously the compass was reflecting the fact that Whistler at approx 48 dd North is a lot closer to the north pole than Sydney at 33dd 48m South and a compass that swings plumb and level in Sydney wont swing plumb and level in Whistler. This means that when the compass was manufactured in Japan the Silva company made a presumption that it would always be used in the Southern Hemisphere and was never intended to be an “all purpose” instrument. I presume that compasses made for the Canadian and North American markets are similarly adjusted and will not work in the southern hemisphere.


    The compass works fine now that I have returned home.


    I have a couple of questions:

    1. Is there any way you can tell from looking at a compass what its effective area of operation is ie are there any codes on compasses?
    2. If my compass works at mid latitudes in the southern hemisphere would it also work at extreme southern latitudes eg Antarctica
    3. Is there any way a compass which works fine in the S hemisphere can be adjusted so that it works fine up north
    4. Is the usual practice if you live down here in the south and wanted to ski, say Alaska or Northern Canada that you would have to buy a compass from a retailer at the place where you were undertaking the journey. That compass of course would then be useless when you returned home.


    Kieran Kelly





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