Archive Intro
 Table Descriptions
 Schema Browser
 Introduction to SQL
 Form Query User Guide
 Query Limits
 How To
 SkyServer Sites
 SkyServer Traffic Page
 Web Browsers
 Contact Help Desk

secondary patch The PT observes a series of secondary patches on a given night, calibrated to the system of primary standards. These patches overlap the 2.5m survey stripes; with the photometry determined for these, we can set the zeropoints of the 2.5m runs.