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    Re: FW: 249 v 229 , Starpath, time tick
    From: Richard B. Langley
    Date: 1999 Mar 15, 08:34 EST

    For info on the various forms of UT, atomic time and civil time (which is
    atomic-time based), see my article on GMT and UT available on various Web
    servers including <http://www.rnw.nl/realradio/features/html/time.html>
    -- Richard Langley
       Professor of Geodesy and Precision Navigation
    P.S.  The time indicated by a GPS receiver on its screen may be a fraction of
    a second delayed due to receiver microcomputer task scheduling.
    On Mon, 15 Mar 1999, Rick Emerson wrote:
    >craig@XXX.XXX writes:
    > > Actually, the GPS (satellite) time is off by about 12 seconds.  Each
    > > manufacturer corrects for this inside the unit.  Accuracy may be affected by
    > > internal errors, but I'm sure it's accurate enough for celestial navigation.
    > >
    >Er, the correct answer is "it depends".  Some receivers make the
    >adjustment between ...what?... UTC1 and UTC2.  While I probably have
    >the names swapped, one's "atomic time" and one's "star" or civil time.
    >The former is so accurate that it can detect small variations in the
    >Earth's rotation which is the basis for the latter.  The cumulative
    >error is the difference between the time as determined by various
    >atomic clocks and the time as determined by timing transits.
    >Adjustments are added or subtracted on the last day of June or
    >December.  A second was added at 23:59:60 on 31 Dec. 1998, for
    >Anyway, the point is that the difference is known and some receivers
    >display atomic time and some display civil time.  The only sure way to
    >know what a given receiver does is to compare its time with WWV or
    >S/V One With The Wind, Baba 35
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     Richard B. Langley                            E-mail: lang@XXX.XXX
     Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
     Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142
     University of New Brunswick                   Fax:      +1 506 453-4943
     Fredericton, N.B., Canada  E3B 5A3
         Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
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