Plotted entries from OPSLOG files in FORS2 report BIAS_struct_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	0.625222797271302
2012-05-16	56064.459745	0.576502841429089
2012-05-16	56064.470173	0.712906032508616
2012-05-17	56065.450203	0.47788635957105
2012-05-18	56066.469392	0.653425160212968
2012-05-19	56067.441297	0.53121701431801
2012-05-19	56067.450593	0.528777768227715
2012-05-20	56068.452563	0.644337864875695
2012-05-20	56068.502068	0.634213265260667
2012-05-21	56069.463784	0.568103490765154
2012-05-22	56070.445073	0.508946526391533
2012-05-22	56070.454340	0.55591307041576