Subjective evaluation is an important component in the evaluation of workstation usability. We have developed and standardized a general user evaluation instrument for interactive computer systems. The methods of psychological test construction were applied in order to ensure proper construct and empirical validity of the items and to assess their reliability. A hierarchical approach was taken in which overall usability was divided into subcomponents which constituted independent psychometric scales. For example, subcomponents include character readability, usefulness of online help, and meaningfulness of error messages. Evaluation on these scales is assessed by user ratings of specific system attributes such as character definition, contrast, font, and spacing for the scale of character readability.