DPRG mailing list archives: [DPRG] digital compass in my car went crazy in Canada

Wed May 21 20:48:27 CDT 2008

If you know a pilot, or just buzz by the local pilot store, you can get
aviation charts. They have magnetic offsets to like 30 minutes.

Here is a section near McKinney TX, the black dotted line is
4degrees 30 minutes East

    http://skyvector.com/#35-27-3-4720-2692

The map is scrollable, have a look around to see how close the
dotted lines are. 5 minutes E is over by gainsville, and 5 30" is
just past Fort Worth.

The magnetic variation changes daily, not enough to worry about,
maybe 1 degree every 3 years, but over time it adds up.

On Wed, May 21, 2008 at 4:10 PM, Dave Hylands <dhylands at gmail.com> wrote:
>>  >  Hi David,  I noted a reading bias towards east until well south of the Canadian
>>  >  border. So I was heading due S but the compass kept reading SE. I wonder how
>>  >  these devices work in Canada? Maybe they only sell them with a GPS receiver.
>
> Here's a good picture that shows the declination for various
> geographic locations:
> <http://en.wikipedia.org/wiki/Image:IGRF_2000_magnetic_declination.gif>
> (obtained from this page: <http://en.wikipedia.org/wiki/Geomagnetism>
>
> My interpretation of this is that anywhere along one of the lines will
> give the difference between magnetic north and true north.
>
> So you can see 10 degrees of difference between southern California
> and Vancouver, BC
>
> --
> Dave Hylands
> Vancouver, BC, Canada
> http://www.DaveHylands.com/
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