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    Re: Differences between GPS and WWV time
    From: UNK
    Date: 2001 Jun 22, 1:26 PM

    Robert Owens [mailto:tugly@NEOSOFT.COM] asked:
    > Has anyone noticed a difference between GPS and WWV time. I hear some
    > display a different time  depending on software.
    The GPS system broadcasts time as a week number (where Week 0 began
    at 00:00:00 6 Jan 1980 UTC) and seconds-of-week. Somewhere else in the
    broadcast message is the current difference between this strict
    sequential count and UTC, since UTC has had a dozen or so leap seconds
    inserted since the beginning of the GPS epoch. All but the most
    primitive receivers correctly apply the leap second correction.
    However, as Dan Allen noted, receivers' internal clocks often drift,
    and shouldn't be trusted until the unit is tracking.
    An interesting variation on the "Y2K Bug" of recent memory was GPS week
    roll-over. The week field is 10 bits long, so in August 1999 it rolled
    over from week 1023 to week 0. Some early GPS receivers needed software
    updates or some other intervention in order to cope.
     -- Peter

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