Are the answers right?

• The overlaps between images are a rigorous test of our internal consistency. With the CTIO 0.9-m we get to a few milli-mags.
• We have done photometry of standard fields, as though they were data,and this suggests we typically get to within 2% of the standard system.
• Checking one catalogue against another suggests our relative positions are good to 0.05 arcsec. Correlations with catalogues like 2mass and SuperCosmos give RMSs of around 0.17 arcsec, presumably driven by their accuracy.