Allan variance as a function of time. This observation was performed as a three-day drift scan of Cas A pointing at ~ 79° elevation due south. The signals from the daily Cas A passages have been removed. In the lower panels also a few strong signals have been removed that occurred on a solar day basis (those could be due to any kind of human activity such as a transmitter that is scheduled to turn on or increase its power for a short while every day, or artificially induced changes to the instrument environment such as variations in the AC power grid).