The local time sources are a Garmin GPS 18 LVC
and a Conrad DCF 77 receiver.
DCF77 data is clipped to ± 99 ms. Without clipping the graphs would contain spikes up to an hour (usually during thunder storms).
I replaced ntp1.nl.net with ntp2.oma.be, since ntp1.nl.net was way off.
I removed ntps1-1.cs.tu-berlin.de, since it was way off.
There is no NMEA daily offset graph.