FieldSystem Contains information about the systems of field centres used in the SSA. Survey Contains information about the Schmidt photographic surveys in the SSA. Plate Contains information about each survey plate measurement used in the SSA. Detection Contains individual plate detections for every plate in the SSA. JunkDetection Contains a subset of the entries in Detection that are flagged as junk Source Contains merged sources for every field in the SSA. Field Survey field information for the SSA. IsoCalVersion Information concerning all isophotal photometric calibrations in the SSA PrevIsoCal Previous isophotal photometric calibration coefficients for all plates CurrIsoCal Current isophotal photometric calibration coefficients for all plates Table of Galactic co-ordinates for the merged table Source.