[ntp:questions] Quick sync between two computers not connected to the internet

Dave Hart davehart at gmail.com
Fri Mar 19 19:04:30 UTC 2010

On Mar 19, 18:21 UTC, a xs4all user wrote:
> Of course you should not configure them to follow another in both directions.
> When the second computer follows the first, there is nothing instable
> or wrong going on.  You can even pick the computer that has the most
> stable clock before configuring them.

That's tricky without internet or other access to a stable frequency
source.  The machines in question do not and never will have access to
the internet.

> He only requires the time to be the same on both computers.  There is
> nothing that a GPS receiver will add to the system to make this easier
> than without it.  But of course it adds complexity and requirements.

There's one thing -- irrelevant if w32 time sync is close enough, but
ntpd has a 500ppm limit on frequency correction.  Depending on the
number of machines (two here) and each machine's normal frequency
error, it may be necessary to get the source machine's frequency
closer to correct to bring it in the range the other can correct.
This is unlikely to be a problem with a couple of machines each within
125ppm, for example, but get unlucky with a few hundred ppm positive
on one and negative on the other, or add more machines to the brew,
and your chances of having problems using an errant frequency standard
(the source machine's uncorrected clock) go up.

Dave Hart

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