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Subject: [Nml] GPS Time
From: Daniel K. Allen (Visual C++) (danallen@XXX.XXX)
Date: Mon Mar 15 1999 - 14:38:41 EST
With my old Garmin GPS 40 I noticed that occasionally the displayed time on
my GPS was up to 1.5 seconds off of WWV. More recent Garmin receivers seem
to be better.
One other potential "gotcha" with GPS receivers: until the satellites are
locked on, the displayed time may be WAY off. The built-in clock is
terrible. I guess Garmin assumes you will always have the satellites
around, but before lock on I have seen the displayed time off as much as a
MINUTE or more (especially if the GPS has been sitting unused for a few
months). Once the 3rd satellite appears, then the time jumps to the "real"
time.
We need more accurate clocks available. A few watch manufacturers in the
1980s made "Twin-Quartz" watches (Seiko Lasalle and Omega) which were
thermally compensated and would not be off a single second in a year. If
they were off from WWV, it was usually because a leap-second had been
inserted! Alas, I do not own either watch (a friend has had these), but I
wish somebody would make a twin-quartz chronometer again with ultra accurate
time.
Dan
-----Original Message-----
From: Richard Langley [mailto:lang@XXX.XXX]
Sent: Monday, March 15, 1999 5:34 AM
To: Rick Emerson
Cc: navigation@XXX.XXX
Subject: Re: FW: [Nml] 249 v 229 , Starpath, time tick
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.
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