[time-nuts] Us Time Nuts and... Wrist Watches.

jimlux jimlux at earthlink.net
Mon Jan 3 16:23:52 UTC 2011

Tom Van Baak wrote:
> Steve,
> After you're done chuckling, note that one man's "utterly
> insignificant" is another group's passion.
> A 6 foot person vs. 98 million miles is 6 / (9.8e7 * 5280),
> or 1.16e-11, a unitless number that's well within our range
> of expertise and fascination; neither utterly nor insignificant.
> The number is half a day of a 10811 aging spec; a month
> of rubidium frequency drift; a cesium in need of big C-field
> adjustment; one microsecond per day; 0.1 Hz at 10 GHz;
> the typical short-term peak-to-peak frequency stability of
> a TBolt, etc.
> To further appreciate the level at which we work & play, if
> 1e-11 is the ratio of a man standing compared to the sun,
> then 1e-12 is about 6 inches (like waving your hands) and
> 1e-13 is about half an inch (like blinking your eyes).

I find I have to make these sorts of comparisons when pointing out how 
hard it is to do these kinds of things.  Someone blithely says, Oh, for 
our gravity science we want 1E-16 Allan deviation over 1000 seconds at 
32 GHz in the round trip measurement from earth to Jupiter and back. 
Jupiter is about 6E8 km away, so a 1E-16 measurement is comparable to 
measuring to about 1E-5 km or around 1 cm.

That's pretty impressive.

And, then, you say, Exactly how will you prove that your box can make 
the measurement to that precision?

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