A unified approach to improved usability can be identified in the works of Gilb (1981, 1984), Shackel (1984), Bennett (1984), Carroll and Rosson (1985), and Butler (1985). We term this approach “usability engineering,” and seek to contribute to it by showing, via a product development case study, how user-derived estimates of the impact of design activities on engineering goals may be made. 1

A unified approach to improved usability can be identified in the works of Gilb (1981, 1984), Shackel (1984, Bennett (1984), Carroll and Rosson (1985), and Butler (1985). We term this approach "usability engineering," and seek to contribute to it by showing, via a product development case study, how userderived estimates of the impact of design activities on engineering goals may be made.'