The quality control group at ESO monitors a variety of instrument parameters such as zeropoints, efficiencies, read-out noise, etc. These measurements can be plotted or listed at http://archive.eso.org/bin/qc1_cgi?action=qc1_browse_instrume.

A description of the parameters that are regularly trended is available for each instrument at

http://www.eso.org/observing/dfo/quality/<INSTRUMENT>/qc/qc1.html

where <INSTRUMENT> is the capitalized string for one of the instruments, CRIRES, FORS1, FORS2, GIRAFFE, ISAAC, HAWKI, KMOS, SINFONI, UVES, VIMOS, VISIR, XSHOOTER, AMBER, AMBER, MIDI, VIRCAM, OMEGACAM, or VIRCAM.