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name	type	text
USNO	External	This table contains all of the objects in the USNO-B catalog which match an SDSS object inside the data release boundary. However, because this matching was originally done with USNO-A, many new fields from the newer USNO-B are NOT in this table (such as the POSS-II matches), see the USNOB table. There are two tables of proper motions provided in the CAS. This table (USNO) is the USNO-B1.0 catalog, for which the reference is Monet et al. 2003, AJ, 125, 984. This is simply the closest matching USNO-B1.0 object, and was used in some target selection. The second table is ProperMotions, which is the proper motion after recalibrating USNO-B1.0 against SDSS astrometry, and then combining the recalibrated USNO-B1.0 and SDSS astrometry. The statistical errors for this catalog are roughly 20-30% less than those in USNO-B1.0, however the systematic errors are greatly improved, being much less than 1 mas/year. The reference for that catalog is Munn et al. 2004, AJ, 127, 3034.