Plotted entries from OPSLOG files in FORS2 report BIAS_med_master, plot 2 (data set parC1lm):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2013-05-14	56427.429164880000000	195.66667175293
2013-05-15	56428.440190530000000	196
2013-05-16	56429.348795310000000	196
2013-05-19	56432.463350830000000	195.66667175293
2013-05-20	56433.437120250000000	195.33332824707