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

Rob nomail at example.com
Mon Apr 18 16:28:56 UTC 2011

Chris Albertson <albertson.chris at gmail.com> wrote:
> 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.

You assume that your measurement scale is very coarse.  Your reference
is seconds and you can only measure plus or minus one second.
But that is not true in NTP with a local reference clock.  It can measure
to microseconds or even nanoseconds.

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