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Zip, baring some kind of local phenomon, what you observed is called DIP
and there are charts of it just like there are charts of magnetic deviation
(and they are often the same chart).   Any good nautical chart store should
have one for the world.   Dave
 
Dave Gomberg, role model for those who don't ask much in their fantasy lives.
GOMBERG@UCSFVM  Internet node UCSFVM.UCSF.EDU             fax-> (415)731-7797