How do you design gears for surface durability using the AGMA approach?

AGMA surface durability uses contact stress equation: sigma_c = Cp x sqrt(Wt x Ko x Kv x Km x Cf / (d x F x I)), where Cp is elastic coefficient, Wt is tangential load, Ko is overload factor, Kv is dynamic factor, Km is load distribution factor, Cf is surface finish factor, d is pitch diameter, F is face width, and I is geometry factor. Compare with allowable stress: sigma_c_allowable = Sc x Cl x Ch / (Kt x Kr), where Sc is contact endurance strength, Cl is life factor, Ch is hardness ratio factor. Design iterations balance bending and surface strength.