Quote Originally Posted by albada View Post
Looks to me like K = Gmin/Gbar. Or am I misunderstanding something?
Anyway, do you know if Gbar was measured over the range of the scene, or if it was a fixed 1.5 in log H units?
That's the equation and that's how 0.3 was determined. Gmin is what Jones calls the limiting gradient and it does represent the first excellent print speed point or print judgment speed. It's point M in the curve.

first excellent print parameters.jpg

Jones says Gbar is the average gradient of the used portion of the characteristic curve. Later in the paper he does define it as 1.50.