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    Re: GPS & Magnetic Bearings
    From: Rodney Myrvaagnes
    Date: 2003 Feb 9, 19:27 -0500

    On Mon, 10 Feb 2003 08:53:27 +1100, Peter Fogg wrote:
    >Brooke Clarke wrote:
    >> ... the magnetic deviation if ...
    >> Jared Sherman wrote:
    >> ... the GPS ... deviation data ...
    >I'm not sure if this is due to different countries using different 
    terminologies but I learned that the compass difference due to the magnetic 
    poles not being aligned with the geographic poles is called compass variation 
    and local effects (like an iron engine block) about the vicinity of the 
    compass is known as compass deviation.
    >So: GPS can have no idea of compass deviation (?) but may, we are learning, 
    have various built in systems to correct for compass variation (?). I guess 
    the real bottom line is that GPS may indicate true bearing which is a mighty 
    useful thing to know.
    You are correct, but since the deviation doesn't affect the GPS it has
    no use for deviation data. If its variation table is still good it will
    be able to show a deviation-free magnetic course. It will always be
    able to show true course if the vessel is moving.
    Rodney Myrvaagnes         NYC                       J36 Gjo/a
    "WooWooism lives"  Anon grafitto on the base of the Cuttyhunk breakwater light

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