0.20. Ifthe calculations have shown the Pfc to be something other 20%, a correction factor must be applied to the CU.
Correction factors can be found in Table 8-6of the Data Section
Since it would be impractical to generate tables that cover all reflectances, interpolation of the tables is required. Linear interpolation is sufficient for this type of calculation and least time consuming. Refer to the examples can be found in reference 8.