This Code provides procedures for the conduct and reporting of performance tests of flue gas desulfurization systems. The performance of a flue gas desulfurization system (FGDS) is defined to be the characterization of inputs and outputs that may include, but is not necessarily limited to, the following: (a) Percent SO removal (%R), (b) Reagent Ratio (RR1 or RRR), (c) Energy/power consumption, (d) Water consumption and characterization, (e) Reagent consumption and characterization, (f) Waste/by product production and characterization, and (g) Availability and Reliability. Availability and reliability of the FGDS are outside the scope of this Code. This Code also contains supplementary information on (a) Types of FGDS, (b) PTC 40 Test Method, (c) FGD data determination Forms, (d) Quantity measurement of solid waste, and (e) Example application.