Equation max PE = .5(D) ABS(t-p)/p
PE - parallax error
D = objective lens dia
ABS absolute value
t-p = target distance - parallax distance
So your 40 mms scope/150 yard parallax setting
@400 .5x40x250/150= 33.3mm or 1.311 inches
@200 .5x40x50/150= 6.6mm or .259 inches
@50 yards .5x40x100/150= 13.3mm or .523 inches.
