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
====================================================
2012-02-07	55965.475607	198
2012-02-08	55966.384107	198
2012-02-09	55967.455193	198