Fig 1. USNO 'B' Magnitude Error f(Magnitude)
Red = USNO - Calibrated
Yellow = Best Fit: Y = +1.47 -0.112 * B_cal
Y vertical Tick = 0.1 magnitude
Offset for Magnitude 14.0 'B' = -0.10
Error cancels for Magnitude 13.1

Fig 2. USNO 'R' Magnitude Error f(Magnitude)
Red = USNO - Calibrated
Yellow = Best Fit: Y = -1.53 +0.083 * R_cal
Y vertical Tick = 0.1 magnitude
Offset for Magnitude 14.0 'R' = -0.37
Error cancels for Magnitude 18.5

For any comment, contact Jean-Claude PELLE