This paper introduces a method for evaluating decision aids for nuclear power plant operators. The method involves a two-stage process of classification and analytical evaluation of display form and content. The classification scheme relates each specific aid to one or more general decision-making tasks. Evaluation then proceeds using a normative top-down design process based on the classification scheme by determining or deducing 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 identification of the training and display features necessary to ensure understandability. 7 refs., 4 figs., 1 tab.