Re: Which clock to trust?

Chris Wyatt. (spacenaut@jaycom.net.au)
Thu, 17 Sep 1998 13:02:23 +1000

Hello See-Sater's,

Robert G Fenske Jr wrote:

> On Mon, 14 Sep 1998 dmbrierley@taz.dra.hmg.gb wrote:
> > I've been following this thread, and I fail to see how anyone can get
> > an accurate time over the Web, with uncertain delays in transmission
> > and nodes.  Either a radio signal or the 1-900 number is preferable.
>
>         Is is quite possible to get times with 10s of milliseconds.  The
> NTP (Network Time Protocol) and associated programs have a lot of research
> and developement behind them to handle this kind of time transfer and
> thus to properly account for variable transmission delays, local clock
> jitter, and local frequency instability.  I have my office PC running an
> xntp client and it usually reports offsets of less than 50 milliseconds (I
> have no way to verify this though).
>

I use a Mac & use the application program "Vremya" for NTP time adjustments, it
comes with a list of NTP servers. I have found it consistent with its updates of
my system clock time, my computer is about 2.5 secs fast per day. This has stayed
the same even though I have changed from a USA based server to one in nearby
Hobart Tasmania.

Also don't forget your personel reaction time as it will be close to the time
differences talked about in earlier mails. Therefore any timings better than 0.5
sec would have to be done by some sort of machine.

The latest version of this easy to use software is available from
http://www.lava.net/~kirill/software/vremya.html

Regards,

Chris Wyatt, Lat. 36.7764S, Long. 144.2411E, elev. 240m