[Fwd: Re: [ntp:questions] Re: drifting on crystal]

Alain alainm at pobox.com
Thu Jan 13 23:50:35 UTC 2005


> NTP does exactly that.  It measures both the frequency and phase (time) 
> error of the local clock and attempts to correct both.  When you lose 
> synchronization,  your local clock should be ticking at very close to 1 
> second per second.  The problem is that, over time, the frequency of the 
> crystal oscillator changes depending on the temperature, the supply 
> voltage, the age of the crystal, the phases of the moon and the whims of 
> the gods.  The local clock is not going to suddenly start gaining or 
> losing thirty seconds per day;

I am not an expert in NTP, but I can tell you about cristals: Some
cristals are *much* better than others. The difference is basically
about quality an can even be inporoved with temperature stabilyzed ones.

I check my drift files often in two machines: an old P200 (firewall) an
drift is around 350 and varies a lot (one day I got 270!), the other
machine is a Toshiba notebook, drift is between 25 and 27. As you can
imagine the the drift *fluctuation* is the problem.

I don believe that drift is calculated over a one-day period, it is the
only thing that could improve accuracy as the day's temperature cicle
tends to repeat. This can be a suggestion for future improvement.

Alain
PS: I believe that in some Motherbaord the on-board crystal could be
changed to a temperature stabilyzed one, This could make NTP keep a very
very stable time.




More information about the questions mailing list