Subject: RE: NJ-NY-PA<br/>
Date: Jul 06, 2005 @ 14:34<br/>
Author: Ron McConnell (&quot;Ron McConnell&quot; &lt;rcmcc@...&gt;)<br/>
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<div id="ygrps-yiv-1726016059"><a rel="nofollow" target="_blank" href="mailto:spookymike@...">spookymike@...</a> writes,<br/>
&quot;I revisited NJNYPA on July 4. ...<br/>
Trifinium:  <br/>
 <br/>
&lt;<a rel="nofollow" target="_blank" href="http://topozone.com/map.asp?z=18&n=4578239&e=525470&s=25&size=s&u=1&lay">http://topozone.com/map.asp?z=18&n=4578239&e=525470&s=25&size=s&u=1&lay</a><br/>
er=DRG25&gt;&quot;<br/>
<br/>
Interesting.<br/>
Something on the map legend caught my eye.<br/>
It shows the magnetic declination to be 0º there.<br/>
Here in Chester, NJ, 39.6mi/63.8km south <br/>
it&#39;s about 13ºW in 2005. <br/>
It&#39;s about 13º W at NYNJPA, too.<br/>
Actually 13.2º by the World Magnetic Model [WMM]<br/>
but the model only claims +/- 1º.<br/>
<br/>
Magnetic declination does change with time.<br/>
When I was a Boy Scout learning to read maps<br/>
in southwest Virginia 50 years ago,<br/>
the magnetic declination there was nearly 0º.<br/>
So I didn&#39;t learn to correct the compass reading<br/>
to find true north in general.  :)<br/>
The WMM verifies my recollection for 1955 in swVA. <br/>
Now the declination there is about 5º W.<br/>
The value at NYNYJPA was about 12º W 50 years ago.<br/>
I doubt it&#39;s been 0º for a long time.<br/>
So don&#39;t trust the magnetic declination values<br/>
on the map either.<br/>
<br/>
FYI, the magnetic model is built into my freeware GCGC<br/>
great circle/geodesic program on my web site.<br/>
<br/>
Cheers,<br/>
<br/>
Ron McC.<br/>
<a rel="nofollow" target="_blank" href="mailto:w2iol@...">w2iol@...</a><br/>
<br/>
Ronald C. McConnell, PhD<br/>
<br/>
 WGS-84: N 40º 46&#39; 57.9&quot;  +/-0.1&quot;<br/>
         W 74º 41&#39; 21.3&quot;  +/-0.1&quot;<br/>
         FN20ps.77GU96 +/-<br/>
         V +5058  H +1504<br/>
<br/>
 &lt;<a rel="nofollow" target="_blank" href="http://home.earthlink.net/~rcmcc">http://home.earthlink.net/~rcmcc</a>&gt; <br/>
<br/>
<br/>
I was gratified to be able<br/>
to answer promptly, and I did.<br/>
I said I didn&#39;t know.<br/>
 - Mark Twain</div>