Plotted entries from OPSLOG files in FORS2 report BIAS_med_master, plot 3 (data set parC2r):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2013-05-17	56430.361892010000000	10.4
2013-05-19	56432.463350830000000	10.4
2013-05-19	56432.464688940000000	10.4
2013-05-19	56432.466623530000000	10.4
2013-05-20	56433.437120250000000	8.8
2013-05-21	56434.063042600000000	10.3
2013-05-21	56434.128274050000000	10.4
2013-05-22	56434.952106410000000	10.6
2013-05-22	56434.957291250000000	10.6
2013-05-22	56435.381387930000000	10.6
2013-05-22	56435.382723720000000	10.6
2013-05-22	56435.384645930000000	10.6
2013-05-24	56437.459517320000000	9.4