Steam Turbine Efficiency

I came across an old quick method for estimating steam turbine efficiency (click picture to enlarge and/or download):

Condensing Turbine Efficiency = A x C x E

Non-condensing Turbine Efficiency = B x C x D x E

Note: Efficiencies of turbines below 500 hp usually are in an efficiency range of 30 to 50%.

In your experience, does it look accurate?