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Subject: FW: [Nml] 249 v 229 , Starpath, time tick
From: Rick Emerson (rick@XXX.XXX)
Date: Sun Mar 14 1999 - 23:05:39 EST
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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