Blog post: swansont: Not That Kind of Atomic Wristwatch

No, this is not one of the pretenders that link up to NIST's atomic time via a radio signal.

$12,000 watch has its own built-in atomic clock

I link to this article because it actually mentions USNO, but there's the original, which mentions it's made (or will be made) in Switzerland, meaning this is probably not just a Symmetricom CSAC that's been marked up with a counter and a display attached, but it's undoubtedly the same technology.

This watch actually points to a problem in timekeeping, that there are two elements one must worry about: telling the time, and disseminating the time. Having a great clock is not particularly useful if you can't transfer the information to anyone, so there is a dual, usually parallel effort to improve clocks and to improve time transfer. Time transfer can't lag too far behind timekeeping or else there's no point in pushing the boundaries.

Here we have the time transfer problem in reverse. If the input is the stem and you have to look at a display (or listen to a voice) to get the time, it is going to be limited to the feature of not gaining or losing a whole second over some long interval. Which goes out the window because you have to reset it when you change the batteries. The watch really doesn't require or exploit its precision, so why? It's really nothing more than an expensive trophy, while some pretty incredible technology is basically wasted. And an analog display? I'd want a digital one that showed the time to better than a second.

However, this does point out the ridiculousness of an episode of Person of Interest from last season, where a very rich guyâ„¢ supposedly had a watch that kept time to the nanosecond. 1 second in 1000 years is roughly a part in 10^10, so that's not even a microsecond per day.
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