Plotted entries from OPSLOG files in VIMOS report BIASLEV, plot 1 (data set parQ2lo):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2013-05-17	56430.368506540000000	200
2013-05-18	56431.269702380000000	199