Plotted entries from OPSLOG files in VIMOS report BIASLEV, plot 4 (data set parQ1hi):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2013-05-17	56430.370784690000000	209
2013-05-18	56431.271973240000000	209