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#5151 - 04/03/02 12:25 AM Re: So I am an idiot--wanna make something of it?
Anonymous
Unregistered


ROFL--Chris, may be the wrong forum, but I GOTTA ask. Did you REALLY reply "Hanging a left, sir!" ? That has got to be an story enhancement, right? It is really too perfect. I have been laughing all day.

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#5152 - 04/03/02 01:40 AM Re: So I am an idiot--wanna make something of it?
johnbaker Offline
old hand

Registered: 01/17/02
Posts: 384
Loc: USA
As I understand it, the compass needle is magnetized so that it will point to the large iron deposit in the earth, the magnetic north pole, which is near the earth's true north pole. Compasses are regularly stored & carried in proximity to other products made of ferrous metal all without apparent effect. Compass manuals do not warn of any such hazard. Indeed vehicular compasses are made with adjustments for biases due to nearby steel & electromagnetic fields. In normal use compasses do not seem to be particularly susceptible to permanently biased readings due to minor storage influences. I'm a lot less confident about what happens when they're subject to powerful magnetic fields.<br><br>When taking compass readings, it's a good idea to test for how much influence the steel products you're carrying cause. Moving the compass towards & away from metal items indicates their range of influence. Knives, multitools, handguns, magazines, & long guns are commonly carried influences. The influence seems to dissipate around 6" from the ferrous metal object. YMMV.<br><br>You may want to try your own experiments. BSA stores offer a number of inexpensive books on compasses & orienteering. A lot of other vendors such as REI, Sports Chalet, & Cabela's carry similar materials. <br><br>John

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#5153 - 04/03/02 04:57 AM Re: So I am an idiot--wanna make something of it?
Anonymous
Unregistered


If you are like me, you need to watch out for the steel elements (e.g., screws) in my eyeglasses frame - a factor if I get real close to the compass trying to get a very precise reading.<br><br>Also, look out for the local geology. I have seen a compass carried on iron rich basalt fields go nearly 70 degrees out because of the local attraction of the rocks.

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#5154 - 04/03/02 06:29 AM Re: So I am an idiot--wanna make something of it?
Trusbx Offline
addict

Registered: 01/16/02
Posts: 397
Loc: Ed's Country
Nope.<br>As far as I know, compasses have no 'memory' per se.<br>Also (correct me if i'm wrong) they will not lose their efficacy unless their magnetism has been affected by a stronger magnetic field.
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Trusbx


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#5155 - 04/03/02 07:38 AM Re: So I am an idiot--wanna make something of it?
johnbaker Offline
old hand

Registered: 01/17/02
Posts: 384
Loc: USA
I've been using an inexpensive Casio digital watch for about 10 years. It's still on the original battery! I use the stopwatch function a lot, but not the light. I'm amazed. None of our other watches' batteries have lasted over a couple years. I'm not sure what it signifies, especially in a survival context, but I'm still amazed.<br><br>John

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#5156 - 04/06/02 09:22 PM Re: So I am an idiot--wanna make something of it?
aardwolfe Offline
Old Hand

Registered: 08/22/01
Posts: 923
Loc: St. John's, Newfoundland
> As I understand it, the compass needle is magnetized so that it will point to the large iron deposit in the earth, the magnetic north pole, which is near the earth's true north pole. <br><br>Close, except it's not a "large iron deposit" it's an elecromagnetic field generated by molten metallic materials in the earth's mantle (the molten layer beneath the crust), at least that's according to the latest scientific evidence. (Or at least, according to Time magazine :-0 ) As such, it moves around - on a daily basis, I understand, it moves in an ellipse about 60 miles across, and is currently (no pun intended) moving northward at the rate of about 10-15 miles per year. <br>(see http://www.geolab.nrcan.gc.ca/geomag/e_nmpole.html)<br>But the bottom line is, the earth is a giant magnet (or electromagnet) and the compass needle lines up with the lines of magnetic flux that the earth creates; hence the compass needles points north (or south).<br><br>I can actually outdo the original poster - I had a cheap dashboard-mounted compass that I bought for my car, and I was using it to demonstrate to a group of cadets how to find North. Well, all the other methods we were using said N was *that* way, and my dashboard compass said N was *this* way, 180 degrees out. I concluded that the thing was hooped and threw it out (it only cost a couple of bucks). Only later did I realize that the compass was designed to be read from the side, not the top. Thus, when you were facing N, the "N" would be facing you - i.e. the "N" pointed South, not North. <br><br>This may not make sense unless you buy one and see for yourself. But trust me - if the compass you're using is designed to be read from the side (as most small airplane compasses are), don't try reading it from the top, even if you can, because chances are you'll be 180 degrees out.<br><br>That mistake could result in a very bad day; I'm truly thankful that I figured it out while teaching cadets and not trying to navigate my way to safety after a plane crash.
_________________________
"The mind is not a vessel to be filled but a fire to be kindled."
-Plutarch

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#5157 - 04/07/02 08:46 PM Re: So I am an idiot--wanna make something of it?
johnbaker Offline
old hand

Registered: 01/17/02
Posts: 384
Loc: USA
Aard,<br><br>Thanks for the clarification & info.<br><br>By the way, what is "St. John Ambulance Brigade"?<br><br>John

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#5158 - 04/08/02 03:08 AM St John Ambulance brigade
aardwolfe Offline
Old Hand

Registered: 08/22/01
Posts: 923
Loc: St. John's, Newfoundland
johnbaker;<br><br>What is St John Ambulance? Basically, it's the oldest volunteer service organization in the world (at least, by some reckoning :-). It started out as a religious order that founded a small hospital in Jerusalem in 600 AD. Currently, it's a world-wide (mainly British Commonwealth, I think, but not exclusively so) non-denominational organization (i.e. no religious affiliations) that deals with various aspects of First Aid and hospital care. St. John Ambulance provides First Aid training; mainly a 1-day Emergency course, a 2-day Standard course, and a 3-day Extended course. There are a number of other courses - Advanced First Aid (equivalent to the EMR level), Wilderness First Aid, We Can Help (aimed at 6 to 10 year olds), and others. The Brigade is a volunteer arm that provides First Aid coverage for local events. I'm the Training Officer for a small cadet division (most of our cadets are girls aged 15 to 16 currently). <br><br>For more information:<br><br>St. John Ambulance of Canada : http://www.sja.ca/<br><br>St. John Ambulance of in the UK : http://www.sja.org.uk/<br><br>My own brigade (Calgary, Alberta) : http://www.cadvision.com/stjohnam/home.htm<br><br>For information about our cadet program in particular, and SJA in general, this is an excellent site maintained by an Ontario (Canada) cadet division: www.cadetsonline.ca<br><br>Hope this answers your question. :-)
_________________________
"The mind is not a vessel to be filled but a fire to be kindled."
-Plutarch

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