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From: David Magda <dmagda@ee.ryerson.ca>
Date: Wed, 16 Jun 2004 20:38:32 -0400
To: Harlan Stenn <Harlan.Stenn@pfcs.com>
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Subject: Re: NTPD and SecureLevel 
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On Jun 16, 2004, at 20:03, Harlan Stenn wrote:

>> ntpd(8) doesn't actually change the time by making it 'jump' to the
>> correct time; it slows down or speeds up the rate at which the timer
>> runs at.
>
> Sometimes ntpd will step (jump) the time.

Yes, I've noticed that as well (it appears in my logs). AFAICT there's 
a period of time in which NTPd needs to 'stabilize' and then it slews 
the time after that point. It's been a while since I've looked into the 
NTP algorithm in detail though.

You may want to ask about it in the Usenet group 
comp.protocols.time.ntp for details.