This plot shows the residuals of the lines in 2DMAP (9-pinhole arc) data after the
annealing of the physical model. residx/y_min/max may be large due to
single outliers and are therefore not scored. 
More information can be found in the
<a href="http://www.eso.org/observing/dfo/quality/XSHOOTER/qc/distortion_qc1.html">plot tutorial page</a>.