Plotted entries from OPSLOG files in VIMOS report BIASLEV, plot 2 (data set parQ1lo):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2013-05-17	56430.368506550000000	201
2013-05-18	56431.269702390000000	201