[time-nuts] PPS for NTP Server - How Close Is "Good Enough"?

Hal Murray hmurray at megapathdsl.net
Thu Jun 11 23:20:36 EDT 2015


m.matthew.george at gmail.com said:
> As you can see, the PPM frequency on this Pi is still showing -7.742.  I
> assume that is if it was undisciplined?  I have wondered about that. 

That's the fudge factor needed to make that box keep reasonable time.

At one level, it's the difference between the number printed on the 
oscillator package and the actual frequency coming out of the package.  On 
another level, it's what the kernel measures at startup time.  That 
measurement includes things like spread spectrum (EMI) and bugs in the 
calibration software.

It's usually a good thermometer.


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