In article ,
Craig Prouse wrote:
Dale DePriest wrote:

You need
a table of magnetic variations and interprolate from the table based on
your location as there is no mathmatical model that will provide this
information reliably.

Given a table of magnetic variations at known locations, there are
statistical methods to derive a useful mathematical model. The web site
cited in a previous article provides such a model as a polynomial.

http://williams.best.vwh.net/avform.htm#Var

http://geomag.usgs.gov/chartsdo.html

http://geomag.usgs.gov/models.html

http://www.ngdc.noaa.gov/IAGA/wg8/igrf.html

http://www.ngdc.noaa.gov/IAGA/wg8/table1.txt

http://www.freewarepalm.com/calculator/magcalc.shtml

http://www.garmin.com/manuals/GPSIII...nersManual.pdf page 78 (in document)
(page 88 in pdf file) gives 4 heading adjustment choices: auto magnetic
(using a magnetic field model driven by the current location), true, grid
(driven the UTM locatin) or user magnetic (the user states the desired
adjustment). I suppose that you could use this to include a wind adjustment?!

Other than that; get your aviation weather report and your E6B.

Randolph J. Herber, , +1 630 840 2966, CD/CDFTF PK-149F,
Mail Stop 318, Fermilab, Kirk & Pine Rds., PO Box 500, Batavia, IL 60510-0500,
USA. (Speaking for myself and not for US, US DOE, FNAL nor URA.) (Product,
trade, or service marks herein belong to their respective owners.)