Overall Equipment Effectiveness: consistency of ISO standard with literature

The International Organization for Standardization ISO22400 standard has been published for the purpose of defining a set of Key Performance Indicators (KPI) for manufacturing operations management, and provides two definitions of the Overall Equipment Effectiveness (OEE) indicator. Despite OEE formulation has been well established for thirty years now, the ISO22400 standard versions seem to diverge one from the other and from the original Nakajima's TPM formulation. Moreover, the standard appears to be incomplete, and many relationships among the terms and the definitions are imprecise. In this paper the authors report on the analysis of the ISO22400 OEE indicators and propose a classification of equipment states which can grant the standard consistency with the established OEE expression. Hence, the paper provides the reader with all the indispensable piece of information to practically handle this important KPI without ambiguity.