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    Re: NIST website time accuracy
    From: Douglas Denny
    Date: 2010 Aug 5, 12:23 -0700

    Gary,

    Yes the GPS displayed time on GPS receivers has been discussed before.

    It is an amazing thing to me that the GPS receivers - any of them - can obtain absolute time to a couple of microseconds at worst, and better than that by far mostly, yet the displayed time is all over the place depending on the particular unit used.

    The reason apparently is because the 'client' microprocessor which takes the GPS 'engine's' raw data, does its own independent processing before updating the display - and can be seconds (even up to several seconds has been reported) after the absolute time received.

    My very old first generation GPS Trimble Transpak is always only one second behind the absolute time at the point of an update. So long as it is continuously updating I know it is one second slow.

    The daft thing is - if the raw second pulses from the GPS receiver 'engine' are used as a clock, they are within a microsecond or better.
    You would think it not beyond the whit of man or GPS electronics engineers to make the display correct and to absolute UTC time to a microsecond. Yet they don't. Silly isn't it?

    Douglas Denny.
    Chichester. England.
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