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Subject: Re: FW: [Nml] 249 v 229 , Starpath, time tick
From: Richard Langley (lang@XXX.XXX)
Date: Mon Mar 15 1999 - 08:34:23 EST
Reminder:
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
>example.
>
>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
>WWVH.
>
>Rick
>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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