Here we plot extinction values that are obtained by assuming the
zeropoint is known.

Data obtained on <a
href="http://www.eso.org/observing/dfo/quality/FORS2/qc/zeropoints/zeropoints.html">photometric
nights</a> are plotted in colour. More details can be found on the <a
href="http://www.eso.org/observing/dfo/quality/FORS2/qc/zeropoints/zeropoints.html">plot
tutorial page</a>