Fig 1. USNO 'B' Magnitude Error f(Magnitude)
Red = USNO - Calibrated
Yellow = Best Fit: Y = +1.18 -0.101 * B_cal
Y vertical Tick = 0.1 magnitude
Offset for Magnitude 14.0 'B' = -0.23
Error cancels for Magnitude 11.7

Fig 2. USNO 'R' Magnitude Error f(Magnitude)
Red = USNO - Calibrated
Yellow = Best Fit: Y = +2.28 -0.135 * R_cal
Y vertical Tick = 0.1 magnitude
Offset for Magnitude 14.0 'R' = +0.40
Error cancels for Magnitude 16.9

For any comment, contact Jean-Claude PELLE