The local time sources are a Garmin GPS 18 LVC
and a Conrad DCF 77 receiver.
DCFa data is clipped to ± 49 ms. Without clipping the graphs would contain spikes up to an hour (usually during thunder storms).
2017-10-25: Use ntp0.nl.net, ntp1.oma.be and zeit.fu-berlin.de.
2017-10-28: Added ntp0.rrze.uni-erlangen.de.
2018-01-07: Added $GPRMC based GPS acquired graph.
There are no NMEA daily offset and jitter graphs.