Fig 1. USNO 'B' Magnitude Error f(Magnitude)
Red = USNO - Calibrated
Yellow = Best Fit: Y = -0.44 -0.002 * B_cal
Y vertical Tick = 0.1 magnitude
Offset for Magnitude 14.0 'B' = -0.47
Error cancels for Magnitude -211.9

Fig 2. USNO 'R' Magnitude Error f(Magnitude)
Red = USNO - Calibrated
Yellow = Best Fit: Y = -0.66 +0.032 * R_cal
Y vertical Tick = 0.1 magnitude
Offset for Magnitude 14.0 'R' = -0.22
Error cancels for Magnitude 21.0

For any comment, contact Jean-Claude PELLE