Question about Window Calculation in EnergyPlus

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The question is about Simple Glazing system's angular properties.

In P286 of Engineering Reference(Version: March 23, 2018, Build: 40101eaafd), Step 7. Determine Angular Performance has said that SimpleGlazing system's angular properties will be choosed based on U and SHGC from 28 bins of Transmittance and Reflectance Correlations.

However, in P294 7.7.6.3 Angular Properties for Simple Glazing Systems said that "When the glazing system is modeled using the simplified method, an alternate method is used to determine the angular properties.", and several equation had been given.

I wonder what's the different bewteen these two Simple Glazing Systems, if they are same thing, why they use different calculation method for angular properties?