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    Re: NIST website time accuracy
    From: Lu Abel
    Date: 2010 Jul 25, 09:39 -0700
    Tom:

    You were told 0.4 seconds uncertainty because the site measured some inconsistency in the time it takes to deliver Internet packets to your computer.

    Remember that the Internet is like the Post Office, not the telephone company.  There isn't a unique connection between you and the site you're visiting.   Instead, thousands of servers are dropping millions of packets are into a complex web of paths.   Packets can take different paths to get to you.  Your service provider can experience "traffic jams" in delivering packets to you.   Either will result in delays in packets reaching you.

    As a computer type, I'm impressed by www.time.gov and the fact that it actually does attempt to measure the round trip delay to your computer and adjust the time it displays.  It's not difficult to do, but it also requires some technical forethought to actually build it into the system.  So whoever at NIST designed www.time.gov had the foresight to design in compensation for Internet delays.

    As a side note, I wonder if NIST has it base "uncertainty" set at 0.2 seconds and then adds whatever delay it measures into that estimate.   The reason for my speculation is that when I "ping" big sites, or use internet speed measurement sites like 2wire.com, most of the time I'm told that my delay to these sites is on the order of a few milliseconds.  

    Lu Abel



    From: Tom Sult <tsult@mac.com>
    To: NavList@fer3.com
    Sent: Sun, July 25, 2010 9:13:49 AM
    Subject: [NavList] Re: NIST website time accuracy

    As I go to the site righ now it said correct to 0.4 sec... Interesting.
    Thomas A. Sult, MD
    IntegraCare Clinic
    www.icareclinics.com
    tsult@mac.com




    On Jul 24, 2010, at 8:19 PM, John Karl 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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