Dark frames are taken once per month with <b>1x1 bin</b> for both low and
high gain. The typical exposure time is 3600 sec. The XSHOOTER
pipeline generates master DARKs from input raw DARKs with master BIAS
subtracted. The dark current is computed from the median master dark frame level in ADU.   
For more information see the
<a href="http://www.eso.org/observing/dfo/quality/XSHOOTER/qc/dark_qc1.html">plot tutorial page</a>.