Abstract: Diagnostic apparatus utilized to monitor a steam turbine-generator power plant. A plurality of sensors around the plant provide data to the diagnostic apparatus which utilizes a digital computer to come to some conclusion relative to actual or impending malfunctions in the plant components. The computer utilizes an expert system diagnosis which establishes a plurality of subsystems which are generic and can be applied to any sensor to obtain indications of (a) sensor output movement, (b) validated sensor readings and (c) malfunction indications based on conclusions reached in (a) and (b).