For the last couple of years I've been using a perl program together
with the "grace" graphing program to generate nice plots based on the
peerstats logs from ntpd. Unlike most ntp monitoring tools, which seem
to be aimed at interpreting local data, these tools monitor the offset
of remote peers compared to the local system.

You can see the results at http://www.febo.com/time-freq/ntp/stats

I've finally gotten around to fixing some long-standing problems and
doing a bit of code clean up, and ntp-stats-0.99 is now available for
download from http://www.febo.com/time-freq/tools/index.html.

While it seems to work, I haven't exhaustively tested against all the
possible configuration options (and the code needs linting and cruft
removal). So if you try it out, I'd appreciate hearing how it works for
you, and especially if you've found (and hopefully fixed!) any bugs.

John