NTP Stratum 1 server; CPU Intel Core2 2.4GHz, Linux-3.10.0-327.4.5.el7, ntpd 4.2.8p4@1.3265, Meinberg GPS170PCI
The graphs below updates every 5 minutes. Previous data can be seen by clicking a plot.

Time offset:
10 us additional shift was applied to the actual offset before plotting.
An offset of a clock equals to its time correction, i.e. time = clock + offset.

source: 'ntptime'
The output of ntpq -p query.

NTP related packet traffic:
source: 'ntpq -c iostats'
green: received packets
blue: packets sent

All the graphs are ploted by MRTG. Because negative values aren't allowed, a 10us bias is added to the actual offset to derive the offset graph above. An ideal timekeeper would therefore display a straight line at the 10us level.

K.Sandler, November 2015