Fig 1. USNO 'B' Magnitude Error f(Magnitude)
Red = USNO - Calibrated
Yellow = Best Fit: Y = +2.14 -0.119 * B_cal
Y vertical Tick = 0.1 magnitude
Offset for Magnitude 14.0 'B' = +0.46
Error cancels for Magnitude 17.9

Fig 2. USNO 'R' Magnitude Error f(Magnitude)
Red = USNO - Calibrated
Yellow = Best Fit: Y = +1.12 -0.057 * R_cal
Y vertical Tick = 0.1 magnitude
Offset for Magnitude 14.0 'R' = +0.32
Error cancels for Magnitude 19.6

For any comment, contact Jean-Claude PELLE