[en] This report presents a proposed methodology that involves a two-stage process of classification and analytical evaluation of decision aids for nuclear power plant operators. The classification scheme relates any particular aid to one or more general decision-making tasks. Evaluation proceeds using a normative top-down design process based on the classification scheme and involves determining how various design issues associated with this process were resolved by the designer. The result is an assessment of the understandability of the aid as well as the identification of training and display requirements necessary to ensure understandability. The methodology is illustrated by applying it to the evaluation of an aid designed to support operators in recovery of critical safety functions at a pressurized-water reactor. Two appendices are included. Appendix A contains information collected from manufacturers, developers, and users of operational aid systems. Appendix B is a review of NRC documents and guidelines that might apply to operational aids