Despite apparent success in using formal models to capture principles of human-system interaction, there are few accounts that consider how these results might be applied in practical software development. This paper is based on work conducted within an ESPRIT Basic Research Action (Amodeus-2) investigating means of design expression and transfer. Within Amodeus we are applying formal methods to the analysis of large design spaces. The focus of this paper is on some initial results obtained from the specification of an interactive system for managing audio-visual (AV) connections in an office environment. Our concern is how the specification (and formal methods in general) can be used to address design issues that impact the user interface. We argue that although formal models cannot guarantee that a system will be ‘usable’, they provide a precise design representation which can be tempered and informed by other perspectives.