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AHA! My Rx Problem Explained!



Hasan wrote:

Today, I bought a compass. Guess what? I wasn't even close. Where I thought
I was pointing at 108 degrees with a nice 8 deg squint....well, I was
pointing at 120 degrees and 108 was in the middle of my TREE. Where I
thought I was pointing at 135....I was pointing a lot closer to 150 deg. In
fact 135 was closer to being in the middle of ANOTHER TREE!

Wayne replies:

Don't forget that your compass points to magnetic north which is not usually
the same as true north because the magnetic north pole is NOT located at the
geographic north pole.  Make sure you correct any compass readings with the
magnetic declination for your specific location.  For instance, Boston has a
magnetic declination of 16 degrees West (magnetic north is actually at 344
degrees azimuth).  Seattle has a magnetic declination of 20 degrees East
(magnetic north is at 20 degrees azimuth).  The magnetic declination is
close to zero in Wisconsin, Illinois, western Tennessee, and Alabama.  

Here's a site with blurry magnetic declination maps for most regions of the
world:

http://www.geo-orbit.org/sizepgs/magmapsp.html
<http://www.geo-orbit.org/sizepgs/magmapsp.html> 

The Canadian government has a nice site where you enter your lat/lon and
your magnetic declination is computed.  You can even see how it changes over
the years as the magnetic north pole drifts around Northern Canada.

http://www.geolab.nrcan.gc.ca/geomag/e_cgrf.html
<http://www.geolab.nrcan.gc.ca/geomag/e_cgrf.html> 

Fortunately for Hasan, the magnetic declination is relatively small in Iowa
- less than 5 degrees.  My magnetic declination in grid EN62af (Chicago
area) is only 2 degrees 22 minutes West.  Back in 1980 my magnetic
declination was only 0 degrees 2 minutes.

Wayne Estes W9AE
Mundelein, IL, USA
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