One of the standard procedures applied during rgsproc is a so-called offset
correction which is designed to deal with an additive noise property of
CCDs. Usually, an identical value is used for every pixel in a CCD node.
Since SAS v6, an alternative has been offered that
takes advantage of offset values that have been determined for each of
the individual 
pixels in a node from routine instrumental
monitoring data. These offset data, which form part of the ODF, are
accumulated every 3 revolutions thus also providing each
pixel with its offset history. While experience of this alternative
approach is being built up, it is not offered as the automatic choice
but users are encouraged to try it and let us know
if they are able to endorse the advantages described in early trials (see
Technical report XMM-SOC-CAL-TN-0046 [12]).
The alternative offset method is selected with the withdiagoffset switch
as in the following example :
rgsproc withsrc=yes srclabel=Mkn421 \
srcstyle=radec srcra=166.113808 srcdec=+38.208833 \
withdiagoffset=yes