In general, each scan is scored using a base quality number multiplied by two individual quality factors (score = base * photometric factor * sensitivity factor), as detailed below.

Scans with quality score > 3 are loaded into the database.

• Base quality number (maximum of 10)
• For optimally dithered scans (after 970606n), base = 10
• For scans not optimally dithered (on or before 970606n), base = 5
• Photometric quality factor (maximum of 1.0)
  computed from mult1*mult2*mult3, where result is not to exceed mult4
• Downgraded if number of cal sets in block < 6 (old strategy) or 5 (new)
• Mult1 is computed from sqrt((number of cal sets)/6[or 5])
• Downgraded if dispersion in photometry for field stars> 0.04 mag
• Mult2 is computed from 2 - ((dispersion used)/0.04)
• Downgraded if dispersion in standard star photometry > 0.06 mag
• Mult3 is computed from 2 - ((dispersion used)/0.06)
• Downgraded if repeat differences in overlaps > 0.05 mag
• Mult4 = 1.0 if scatter in overlap differences is <0.050 mag
• Mult4 = 0.7 if scatter in overlap differences is 0.050-0.075 mag
• Mult4 = 0.4 if scatter in overlap differences is 0.075-0.100 mag
• Mult4 = 0.0 if scatter in overlap differences is >0.100 mag
• Sensitivity quality factor (maximum of 1.0)
• Downgraded if probability that sensitivity meets level-1 specs is <75%, as seen on qyymmddh.bg.see.ps plot
• For values falling above 75%, quality factor = 1.0
• For values falling between 50% and 75%, quality factor = 0.8
• For values falling between 25% and 50%, quality factor = 0.5
• For values falling between 0% and 25%, quality factor = 0.3
• For values falling below 0% line, quality factor = 0.1

Scans which would otherwise have higher scores are further demoted if any of the following problems are encountered:

QUALITY 0:   Tiles for rescanning

• Photometric non-repeatability of sci scans:
• >0.10 mag uncertainty in overlaps for any pair of adjacent scans
• Photometric non-repeatability of cal scans:
• Dispersion in photometry of calibration field stars > 0.08 mag
• Large scatter in zero-point determination:
• Dispersion in photometric zero-point fit > 0.04 mag
• Uncertain photometric zero-point:
• Less than two valid calibration intervals
• RA slippage during scan:
• Double images produced (first seen on 970616n)
• Quadrant jumps in J array:
• Connector problems causing severe ADC offsets (first seen on 970714n; corrected on 970925n)

QUALITY 1:   Not for database inclusion, but better than blank sky

• Severely degraded sensitivity:
• "Photometric" data with 0% chance of meeting level-1 sensitivity specs
• Severely elongated images:
• {band}rat2 > 1.17  or {band}rat2 < 0.77 for any band

QUALITY 2:   Also not for database inclusion, but better than quality-1 data

• Galaxy extractions compromised:
• Untracked seeing