This plot monitors the instrumental issue: ZIMPOL shutter.

This plot shows a QC parameter which measures if all planes of the raw frame
data cube are illuminated (low rms over the plane medians) or not (high rms over the plane medians).
The issue is monitored for FastPolarimetry and SlowPolarimetry readmode and
for both camera, which should react syncroneously. 
The issue started on 2016-05-01 and was fixed on 2016-06-01.

More details on the issue can be found on the SPHERE problems page (see
navigation bar) or on the plot tutorial page.