Glossary
DR5 Help
 Site News
 Introduction
 Cooking with Sloan
 FAQ
 
 Search Form Guide
 SQL Tutorial
 SQL in SkyServer
 Sample SQL Queries
 Graphing
 Query Limits
 Searching Advice
 
 Archive Intro
 Table Descriptions
 Schema Browser
 Glossary
 Algorithms
 Web Browsers
 
 Download
 Data Publications
 API
 SkyServer Sites
 
 Contact Help Desk

nametext
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.