This action proposes corrections and updates to test methods and performance specifications for air emission sources subject to 40 CFR parts 60 and 63. The proposed revisions include corrections to testing provisions that contain inaccuracies and errors, updates to outdated test methods, and clarifications. For example, the omitted constant, K2 for equation 4-2 is proposed to be added in Method 4; the definition of centroidal area is proposed to be updated in Method 7E; and an erroneous reference is proposed to be corrected in Performance Specification 2. This action is developed every two years to keep rules up-to-date and to ensure that compliance testing and monitoring are done correctly.