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    Re: NIST website time accuracy
    From: Lu Abel
    Date: 2010 Jul 25, 09:28 -0700
    As explained by another post, they measure the round-trip delay and compensate the delay for that.  Sometimes when I've logged into www.time.gov, I've seen "accurate to" listings higher than 0.2 seconds.   I strongly suspect that that's because they're not seeing a constant delay to your computer, but rather one that jumps around.

    I'd also point out that transmissions from WWV and its siblings also suffer from time delays -- but they can't be measured because there's no way for the receiver to transmit information back to WWV, the way NIST's internet time service can.

    Net-net I suspect that www.time.gov is probably about the most accurate time standard one can get short of a GPS receiver (which, as people pointed out on posts a year or two ago, can have their own problems).   And in any case, more than adequately accurate for celestial navigation.

    Lu Abel


    From: John Karl <jhkarl@att.net>
    To: NavList@fer3.com
    Sent: Sat, July 24, 2010 6:19:42 PM
    Subject: [NavList] NIST website time accuracy

    The U.S. National Institute of Standards & Technology (NIST) quotes a 0.2 second accuracy for their animated clock on their website http://nist.time.gov/timezone.cgi?Central/d/-6/java.

    Given the vagaries of internet transmission times, can anyone tell me how they do this??

    John
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