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    Re: NIST website time accuracy
    From: John Huth
    Date: 2010 Jul 25, 07:59 -0400
    I believe they "ping" the internet connection to establish the round-trip time.   That is to say, if you send a signal to the host and it gets echoed back to you, you divide by 2 to get the one way trip time and then you factor that into the NIST time as a small correction.   Of course, the implication is that the time delay is always the same.

    I tried to check the drift in my wrist-watch using NIST time.   Of course the watch itself has a temperature issue, but I always wear it, and don't put it in freezers, so I'm assuming it's pretty good.   NIST did a good job tracking the drift, and I didn't see a lot of variation from one location to another.    I also checked it against radio broadcast time, which I assume doesn't suffer the delay issue and it works out reasonably well.


    On Sat, Jul 24, 2010 at 9:19 PM, John Karl <jhkarl@att.net> wrote:

    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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