Completeness of USNO-B for high proper motion stars

I test the completeness of USNO-B detections of high proper motion (mu > 180 mas yr(-1)) stars and the accuracy of its measurements by comparing them to the revised New Luyten Two-Tenths catalog of Salim & Gould. For 14.5 < V < 18.5, only 6% of such stars are missing from USNO-B, while another 3% have large errors, mostly too large to be useful. Including both classes, incompleteness is 9%. These fractions rise toward both brighter and fainter magnitudes. Incompleteness rises with proper motion to similar to30% at mu = 1" yr(-1). It also rises to similar to35% at the Galactic plane, although this is only determined for relatively bright stars V less than or similar to 14. For binaries, incompleteness rises from 9% at separations of 3000 to 47% at 10". The proper-motion errors reported internally by USNO-B are generally correct. However, there is floor of sigma(mu) similar to 4 mas yr(-1) below which the reported errors should not be taken at face value. The small number of stars with relatively large reported errors (sigma(mu) greater than or similar to 20 mas yr(-1)) may actually have still larger errors than tabulated.