This manual describes the physical set-up of the computer system and presents several important 'do's and don'ts' intended to prevent the user from damaging the computer or the diskettes. Chapter 3 contains a step-by-step description of how to run the programs and obtain numerical and graphical output. Chapter 4 presents guidelines for interpreting the program output and a discussion of the limits of accuracy of the programs. These programs have been prepared for use with the Apple II plus minicomputer. The Diagnostic Operational Modeling Programs are intended to provide a reliable and rapid means of identifying process limitations and operational deficiencies. Programs for the following ten types of municipal wastewater treatment plants are available: (1) primary treatment, (2) conventional activated sludge, (3) single stage activated sludge for nitrification, (4) extended aeration activated sludge, (5) extended aeration oxidation ditch, (6) contact stabilization, (7) single stage trickling filter, (8) two stage trickling filter, (9) activated Bio-Filter, and (10) rotating biological contactors. These programs allow the option of an anaerobic or aerobic sludge digestion analysis.