The USNO-A1.0 catalog was generated from the U. S. Naval Observatory's digitization of the Palomar Observatory Sky Survey I O and E survey plates for fields with central declination δ ≥ −30°, and from the European Southern Observatory R and Science Research Council J survey plates for fields with central δ ≤ –35° using the Precision Measuring Machine (PMM) located at the Flagstaff Station. It lists positions (α and δ in J2000) and brightnesses (red and blue magnitudes on the parent plate system) for all objects. A flag indicates if the entry also exists in GSC1.1.