are characterised by a `XFieldName` of the form `XXLsmmm-ppc` with a different letter `c=a,b,c,…` in the rightmost position. In some cases it has been possible to combine the event files of repeats (called z-pointings because the last letter in the `XFieldName` is conventionally `z`, e.g. `XXLn000-04z`): z-pointings are by definition considered superior to the individual repeats in the sequence.

![image](fluxfig.ps){width="17.0cm"}

### Astrometric correction \[SecAstroCorr\]

Following the procedure used for XMM-LSS, an astrometric correction was applied to all sources using the <span style="font-variant:small-caps;">sas</span> task <span style="font-variant:small-caps;">eposcorr</span>, applying to all positions in a pointing a global rigid shift (no rotation was applied). The offsets were computed using reference optical catalogues. For XXL-N the CFHT Legacy Survey T007 version from Vizier (catalogue II/317, [@2012yCat.2317....0H]) was used, except for one pointing where the USNO A2.0 catalogue was used and 16 pointings for which no correction could be computed (bad pointings, with few X-ray detections, which are usually ignored by the overlap removal procedure in favour of better repeats of the same pointing). For XXL-S the reference catalogue was from the Blanco Cosmology Survey [BCS, @2009ApJ...698.1221M], except for 11 pointings for which no correction could be computed for the same reasons noted above. The offsets 