Plotted entries from OPSLOG files in FORS2 report BIAS_ron_master, 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	1.38399890663354
2012-05-16	56064.459745	1.39121606379643
2012-05-16	56064.470173	1.40066349829911
2012-05-17	56065.450203	1.38766102123364
2012-05-18	56066.469392	1.39249588261356
2012-05-19	56067.441297	1.38958171986596
2012-05-19	56067.450593	1.39964667035292
2012-05-20	56068.452563	1.38199013723906
2012-05-20	56068.502068	1.38431108715643
2012-05-21	56069.463784	1.38515993456476
2012-05-22	56070.445073	1.37884991666132
2012-05-22	56070.454340	1.3800996636855