Your GPS receiver probably has the magnetic declination listed if you have it set for magnetic bearings and headings. If you are curious and if you want to do a puzzle cache based upon navigating via true bearing, you may want to check out the following sites. All the downloads are free.

For historical and future magnetic declinations in a particular area try this interactive site: http://www.ngdc.noaa.gov/seg/geomag/jsp/struts/igrfGridZip;jsessionid=81F207732F409A799BA4F30F2A5A8E17

For magnetic declinations in a particular area in years 2005 to 2010 for palm software: http://fermi.jhuapl.edu/software.html If you ask for a declination outside the dates it was designed for it will give you a protest message and then calculate the value. I have compared it with the first link as far back as 1929 and found it accurate enough for hand compass work. In the same link you can also download "Navigate" for Palm OS. I listed it in January this year and since then, I have used it for caching and professionaly with great success. It is a "geodetic traverse" and a "geodetic inverse" application.

This message has been edited. Last edited by: nasty george,

Recently I read a short English mystery story called 'The Blue Scarab' which involved finding a buried treasure. One clue was a compass bearing taken a hundred years past.

I was interested in a cache puzzle based on changing declination, but it hasn't changed as much in Georgia as in England.