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    Re: GPS as a time authority
    From: Nicol�s de Hilster
    Date: 2009 Sep 14, 23:13 +0200

    Dear John,
    
    I think pages 30 -31of the following document will answer your question: 
    http://www.allanstime.com/Publications/DWA/Science_Timekeeping/TheScienceOfTimekeeping.pdf
    
    The problem is that you never know for sure which time is displayed on 
    your GPS until you check it against another source. My hand-held GPS  
    performs similar to yours, while my car-navigation GPS shows a 
    considerable error (about 5-6 seconds), while it tells me it should be 
    UTC. I only found out because a series of sun shots - timed using the 
    latter - on a known baseline did not fit within the expected accuracy. 
    Ever since I either use a DCF-clock (Mainflingen) or the hand-held GPS.
    
    Nicol�s
    
    
    JKP{at}obec.com wrote:
    > I think this has been dicussed before, but I'd like to be refreshed on the list's opinion:
    >
    > While assisting the Race Committee at a regatta this weekend, I heard the 
    timekeepers say that they were using "GPS time."  I noted that my $79 
    wristwatch, which I check monthly against the US Bureau of Standards atomic 
    clock (ph: 303-499-7111) and which doesn't lose a second per month, was 8 
    seconds ahead of the Committee's time.
    >
    > I later checked the time shown on my hand-held Gartmin GPS receiver, and it 
    agreed with my watch.  The watch was also still in sync with the Bureau's 
    atomic clock.
    >
    > Question:  Is the time displayed by GPS receivers considered a reliable and 
    spot-on source, up to the requirements of accurate celnav?  I would think 
    that it would be, since the GPS network depends on accurate tracking of the 
    satellites' position at a given time, yet there was that 8-second 
    discrepancy.  Perhaps the Race Committee were simply careless about setting 
    theior clockby GPS.
    >
    > Any thoughts, List Members?
    >
    > -John Parsons
    >
    >
    > >
    >
    >   
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