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    Re: What time is it?
    From: Trevor Kenchington
    Date: 2004 Nov 11, 11:29 -0400

    Thank you, Peter.
    I guess I will check my GPS display against the dial-up time signal from
    Canada's NRC. If it is tracking UTC, then it presumably will continue to
    do so. If it is fast by a good number of seconds, I'll abandon the idea
    of using at a time reference.
    Trevor Kenchington
    Peter Smith wrote:
    > GPS time is the number of seconds since 06-Jan-1980 00:00:00.0 UTC, and is
    > steered to an accuracy of better than 1 microsecond. It is encoded in the
    > GPS NAV message as the number of weeks since 06-Jan-1980 and the number of
    > seconds since the start of the week. As such, it does not include leap
    > seconds, so a naive reading of GPS time would be fast of UTC today (13 or 14
    > seconds, I believe, for the number of leap seconds since 06-Jan-1980).
    > However, elsewhere in the GPS messages it gives the correction, so receivers
    > can display UTC or UTC-derived zone time.
    > Interestingly, on 22-Aug-1999, the 10-bit week number field wrapped around
    > from 1023 to 0, causing some early GPS receivers to lose track of the date.
    > The US Naval Observatory's GPS page at http://tycho.usno.navy.mil/gps.html
    > has some info.
    >  -- Peter
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

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