Remnance effects from previous exposure are measured by subtractin the
redmost interorder flux from the order flux of the redmost order. If
it is above 4.5 there is a high probability for remnance effects.
For more information see the
<a href="http://www.eso.org/observing/dfo/quality/XSHOOTER/qc/dark_qc1.html">plot tutorial page</a>.