1. used a realistic survey scenario but it is not the survey that will eventually be implemented by PS1,
2. used a simplistic weather model,
3. used a S/N-dependent astrometric error that is more appropriate to future surveys with better catalogs (at the onset of operations PS1 will probably use the USNO-B catalog (Monet et al.,2003) which will limit absolute astrometry to worse than 0.1”),
4. not incorporated false detections,
5. used an early version of the MOPS with reduced efficiency compared to the most recent version (80% vs. 100%),
6. not accounted for the camera fill-factor (the fraction of ‘live’pixels on the detector compared to the footprint of the focal
plane on the sky).