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).
I replaced ntp1.nl.net by ntp2.oma.be, since ntp1.nl.net was way off.
I removed ntps1-1.cs.tu-berlin.de, since it was way off.
I replaced ntps1-0.cs.tu-berlin.de by zeit.fu-berlin.de, which is more accurate.
There is no NMEA daily offset graph.