[ntp:questions] NTPD can take 10 hours to achieve stability

Chris Albertson albertson.chris at gmail.com
Mon Apr 18 14:45:03 UTC 2011

On Sun, Apr 17, 2011 at 11:33 PM, unruh <unruh at wormhole.physics.ubc.ca> wrote:

>> NTP works kind of like that.  It uses a set of reference clocks and
>> watches the rate of your local clock relative to the reference
>> clock(s) and depending on details it make time some time
> Nice analogy. If only chrony did not demonstrate that using exactly the
> same time interchange with an accurate clock, the computer can achieve
> usec accuracy within less than an hour. Ie, your analogy simply does not
> hold as a general statement.

The analogy is perfect and applies to all clocks, computer based  and
otherwise.  There is simply no way to match the rate of one clock to
another without waiting until you are able to measure divergence.  The
length of time you have to wait depends on the accuracy which which
you can measure the divergence and your goal for precision.   It
general you devide one into the other to get time.  Now if you have
two programs and one is faster at setting the clocks rate, then you
have an implementation detail.  What I said above defines the minimum
time required.  Of course one would work slower.  The OP's question
was why in theory does it take a long time, and gave no details of his
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Chris Albertson
Redondo Beach, California

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