The upper diagram shows accuracy and stability of the local clock loop. The local loop frequency (lower diagram) is known to be temperature dependent. In the summer you may well observe a correlation to the outside air temperature recorded by our weather station. In the winter there is a weekly rythm of room temperature due to reduction of heating at weekends. (ppm: pulses per minute)

Time and frequency standard deviations roughly follow the respective offsets:

Offset peaks of 1 sec at some days are due to work on the server or to the room cleaning personnel. They sometimes turn the DCF77 radio clock receiver to a wrong direction. 2 sec peaks indicate thunderstorms disturbing the LF radio signal.