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    Re: Da Lurk
    From: Jared Sherman
    Date: 2003 Feb 9, 14:08 -0500

    Fred-
     
    
    GPS knows nothing about steering directions, it only knows the actual course 
    taken by the GPS antenna. If you are steering 340 but making 350 due to 
    leeway, the GPS will only tell you that you are making 350. Or, that the GPS 
    antenna is making 350 so it presumes the rest of the boat is moving that way 
    too. GPS literally "can't" be swung like a compass can.
    
    GPS knows nothing about true/magnetic, unless someone tells it to display one 
    versus the other and gives it deviation information. I'm not sure if that is 
    available from the GPS system (I don't think so) but the deviation data for 
    the world can be stored in ROM and then "generated" by the GPS unit running 
    the current date against that to extrapolate the correct information for the 
    time and position that the GPS system has given it.
    
    There was some discussion...here?...some time ago about one brand of GPS that 
    indeed had a firmware error and was apparently calculating magnetic/true 
    incorrectly. French or English I think--a brand that doesn't appear here on 
    the US market.
    
    
    

       
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