Plotted entries from OPSLOG files in FORS2 report BIAS_fp_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	0.219893553304951
2012-05-16	56064.459745	0.0626566204698878
2012-05-16	56064.470173	0
2012-05-17	56065.450203	0.297825578758636
2012-05-18	56066.469392	0.176031519346731
2012-05-19	56067.441297	0.292536353340434
2012-05-19	56067.450593	0.18104748782127
2012-05-20	56068.452563	0.044754906825597
2012-05-20	56068.502068	0.11135648907872
2012-05-21	56069.463784	0.292720666111504
2012-05-22	56070.445073	0.191258634729945
2012-05-22	56070.454340	0.187450359947959