On Tue, 2008-11-25 at 09:43 -0500, Richard B. Gilbert wrote: [...] > > What's the best way to determine which of our NTP servers provides the > > best local clock? > > Note the difference between each clock under test and the correct time. > Wait seven to ten days and compare these clocks again. The clock with > the least change in the original offset is the "best clock". Note that > this is not fool proof; you might find a situation in which the "best" > clock varies wildly from hour to hour and is only the best "on average". > > A more adequate test would be to set up a server with a GPS receiver and > compare the offset of all the local clocks under test every thirty > minutes over a period of several days. But, if you are going to do > that, you might as well make it permanent and use it for your master clock! > > Consider that the Garmin GPS18LVC has a pulse per second output and > costs less than $100 US. If you can site an antenna with a good view of > the sky, you can have a stratum 1 server of your very own and have the > time accurate to within a millisecond or less. Note that while the GPS > is accurate to 50ns or better the process of getting the time into your > computer may introduce several hundred microseconds of uncertainty.
Interesting... We'd have to run a long cable though, the computer lab has no windows and the roof is the most logical place to put an antenna. I don't think USB will handle that much line loss. It's a single story section of the building so we're probably talking about 100 meters or so to get a view of the sky. I'll need a version that can handle the remote distance. I'll request a purchase but it could be months before we see it. After a bit of googling I found an excellent write-up on how to use one of these for an NTP server [http://time.qnan.org/ "Using a Garmin GPS 18 LVC as NTP stratum-0 on Linux 2.6"] Thanks Richard! ./Cal _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
