This is the instrument performance plot showing deviation from linearity calculated for two MIT detectors of FORS2 (Chip1 and Chip2) in two different read-out modes (High- and Low-gain). We monitor here a difference, at a given ref_level, between the flux obtained from
 2nd order polynomial fit of flux vs. exposure time and the flux predicted by the linear term only, normalized by the polynomial flux.

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Since data taken after 2009-10 rarely reach 60000 ADU we changed this
ref_level from 60000 ADU to 40000 ADU, starting 2009-10.

</font><p><font size="2">The respective reference values are currently identical to the average of measured data points.

</font><p><font size="2">More information can be found on the <a href="http://www.eso.org/observing/dfo/quality/FORS2/qc/detmon_qc1.html">plot tutorial page</a>