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Hi Jared,

It seems that the most accurate watch currently in production is Citizen
"The Citizen", with an accuracy of +/-5 sec a year.

For the use of GPS as time signal, I agree with you on the practical
purpose.

What I mean in my last post is that if you switch on your GPS, well,
just read the position and plot it on the map.

If you use Astronomical Navigation as a backup to GPS, it's because you
expect that GPS could not work at all. So you need an onboard reliable
time source, that is a good quality quartz watch or a quartz marine
chronometer (very difficult to find nowadays), with the daily variation
perfectly known. I agree that you can use the GPS to check your watch
periodically.

Best regards

Pierre Brial


Jared Sherman a ?crit:
>
> Pierre, I have a $10 Timex that has perversely proven to be the most
> accurate watch I own, typically better than 5 seconds a month. It
> embarrasses my old Accutron (once one of the most accurate watches on the
> planet) and my more recent brand name quartz watch.
>
> But the GPS, at $100 comparable to many "good" watches, is displying the
> time from a dozen or more atomic clocks, which would have cost $3-4 million
> EACH for a collective value of 40-50 million dollars worth of time
> sources--without counting the costs of putting them in orbit.
>
> Yes, it is perverse to use the GPS as a time source, but having access to a
> $50 million dollar time source for less than a hundred bucks, that's
> something to seize and not let go of.

   

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