[ntp:questions] Re: ntp servers reporting leap second erroneously?

Danny Mayer mayer at ntp.isc.org
Tue Oct 25 12:27:06 UTC 2005

Martin Burnicki wrote:
> Hal,
> Hal Murray wrote:
>>How fast does Windows normally slew?  I was expecting it to be 500
>>ppm which would take a long time to slew a whole second.
> Maybe the following is a bit nitpicking, but "Windows" doesn't slew the time
> at all.
> Whichever time adjustment service is running, it can modify the tick
> adjustment value under Windows as required/desired. 
> 500 ppm is a limitation which is specific to ntpd, and maybe operating
> systems which implement the kernel clock algorithm developed by Dave Mills,
> which is great, BTW. AFAIK the limitation is with respect to the time
> synchronization algorithm and the stability of the control loops.
> Windows doesn't implement Dave Mills' clock model, and other time adjustment
> services are not limited to the 500 ppm value.
> The article I was referring to can also be found in the NTP questions
> mailing list archive:
> http://lists.ntp.isc.org/pipermail/questions/2005-October/007296.html
> In the log output you can see that the tick adjustment value is temporarily
> changed from 156250 to 78125, so the system time temporarily increases with
> half speed only until the time offset introduced by the leap second has
> been compensated.

I hope you mean *decrease* with half speed. You are adding a second not
subtracting it so the clock needs to slow down.

> Martin

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