Plotted entries from OPSLOG files in ISAAC report ZPOINT_SW_X0, plot 4 (data set p_ZP_KS):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2012-05-18	56065.959194	24.1129264665311
2012-05-18	56065.976885	24.1034485643166