Plotted entries from OPSLOG files in VIMOS report BIASLEV, plot 8 (data set parQ4hi):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2013-05-14	56427.443797850000000	215
2013-05-15	56428.437280020000000	216
2013-05-16	56429.371153450000000	216