Re: how to analyze clock drift

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Mon, 24 Nov 2014 12:30:53 -0800 (PST), brbarkstrom@gmail.com wrote:

> If you want to get time standard information, you can start with the
> very short background piece from Wikipedia:
> 
> http://en.wikipedia.org/wiki/Standard_time_and_frequency_signal_service

The earth radius Re=6_371_000 m. Pi * Re / c where c is the speed of light
299_792_458 m/s is a rough estimation of the delay the signal takes
traveling from the US to EU, ignoring refraction, interference, amplifiers,
encoders/decoders etc. This is catastrophic 67 ms. It could be improved by
statistical processing to, maybe, 10 ms or so. Now compare that with the
resolution of a typical real-time clock, which is >3 ns!

Add here times required to sample the signal, to pass it through the system
layers, and you will understand how poor the thing is for any time
measurement (except maybe for the continental shift times (:-)).

Fortunately, neither global time signals nor NTP is needed for time
measurements, clock drift included.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de