Plotted entries from OPSLOG files in MIDI report REFPIX_SP, plot 6 (data set PBY_SP_ops):
(DATE changes at 21:00 UT or MJD-OBS = xxx.875)
DATE       	MJD-OBS      	values
====================================================
2012-05-21	56069.540336	29.497308
2012-05-22	56070.394711	29.463942
2012-05-23	56071.389039	29.468968