Plotted entries from OPSLOG files in FORS2 report BIAS_med_master, plot 5 (data set parC2lm):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2013-05-19	56432.463350830000000	197.33332824707
2013-05-20	56433.437120250000000	197
2013-05-21	56434.128274050000000	197
2013-05-22	56434.952106410000000	196
2013-05-22	56434.957291250000000	195.33332824707
2013-05-22	56435.381387930000000	196.33332824707