User interface design can be viewed as a two-stage process. Logical user interface design attempts to define the information flow across the human-computer boundary without defining the specific form of dialogue. At this stage user tasks and system functions are the focus of the design process. It can be argued that physical user interface design requires a prior concern with the tasks to be supported if it is to be successful. Physical user interface design addresses the specific form of the dialogue used during human-computer information exchange. SD Scicon's human factors group has developed an operability assessment database tool to support the logical design stage, the use of this tool is described. To support physical user interface design a range of commercially available tools have been used. Experience with these tools is described and the usefulness of different classes of tool to support prototyping is discussed