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RE: [TR] Quest

To: "Randall" <tr3driver@comcast.net>
Subject: RE: [TR] Quest
From: "Mark Hooper" <mhooper@digiscreen.ca>
Date: Wed, 12 Apr 2006 23:11:02 -0400
What will we do with all the antique compasses when the Earth's magnetic field
flips? Can we just put the labels on upside down?

Mark


________________________________

From: owner-triumphs@autox.team.net on behalf of Randall
Sent: Wed 12/04/2006 8:29 PM
Cc: Triumphs@autox.team.net
Subject: RE: [TR] Quest



>  If one were super pedantic, one would point out that Variation is the
> difference between True North and Magnetic North which is very exactly
> determined worldwide by the geological surveying people

Except that the US Geological Survey calls this the magnetic declination,
not Variation.
http://geomag.usgs.gov/

> and marked on maps
> and charts with a date and accompanying information about the the annual
> change of Variation for that epoch as they call it.

Right, but the annual change is only known precisely after it happens.
Anything else is just a projection, subject to error.  There are also
significant short term variations, and even things known as "magnetic
storms" where all h*** breaks loose for a few days.  The link above has an
entertaining plot of the storm of Oct 29-31 2003, and if you poke around on
that site, you'll also find near-real-time plots of the current variation.

> Also in high
> latitudes the angle of Dip (be quiet that dirty minded boy at the back)
> becomes significant.

Of course, until near the magnetic pole there is no horizontal component at
all and your magnetic compass just spins uselessly.

> The thing you have to deal with  concerning your TR compass is Deviation
> which is the difference on any given heading between magnetic
> North and your
> compass reading. This is local to your car

Not necessarily just the car.  There are also local variations, due to iron
ore deposits and whatnot.

> and Randall himself are  theoretical

Gee I always wanted to be theoretical !  Thanks !

Randall


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