Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!ucla-cs!ucivax!orion.oac.uci.edu!ucsd!celit!billd
From: billd@fps.com (Bill Davidson)
Newsgroups: comp.protocols.time.ntp
Subject: precision
Message-ID: <18313@celit.fps.com>
Date: 6 Jun 91 22:26:53 GMT
Organization: FPS Computing Inc., San Diego CA
Lines: 21

I am a little curious about the precision paramter in the ntp.conf
file.  It says in the manual that it should probably not be changed
unless there is a good reason to do so.  What consititutes a good
reason?

Some of the machines we have (including the ones we build but also some
others) synchronize their system clocks to a hardware counter at each
gettimeofday() call and at each tick rather than just blindly adding
"tick" microseconds every tick.  As a result, microsecond precision is
possible.  Admittedly, the only machine which I checked had it's clock
timer crystal spec'd at 0.0025% (or 25PPM).  Also there's the overhead
of setting the system clock and returning from the system call so I'm
not sure it's right to say it's accurate to 1 microsecond.  Maybe it
is.

Does it make any difference anyway when the machines which have the
higher precision aren't even at the lowest stratum level that I run?
I would think that it might not make any difference unless every clock
from a stratum 1 on up in the path had the high precision.

--Bill Davidson