Plotted entries from OPSLOG files in FORS2 report BIAS_ron_raw, plot 4 (data set parC2lm):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2012-05-15	56063.448065	2.8465553998342
2012-05-16	56064.459745	2.8881367170493
2012-05-16	56064.470173	2.89010176730279
2012-05-17	56065.450203	2.86614597241544
2012-05-18	56066.469392	2.89286031928332
2012-05-19	56067.441297	2.87523324298902
2012-05-19	56067.450593	2.87646171994861
2012-05-20	56068.452563	2.87131553576222
2012-05-20	56068.502068	2.88812502481934
2012-05-21	56069.463784	2.85416024348091
2012-05-22	56070.445073	2.85208674546948
2012-05-22	56070.454340	2.8506165116004