sentences:  In the United States, The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and The National Fenestration Rating Council (NRFC) maintain standards for the calculation and measurement of these values.The shading coefficient (SC) is a measure of the radiative thermal performance of a glass unit (panel or window) in a building.It is defined as the ratio of solar radiation at a given wavelength and angle of incidence passing through a glass unit to the radiation that would pass through a reference window of frameless Clear Float Glass.