Abstract

Ease of use or usability is gaining ground as a selling argument. However, designing usable consumer products still remains a complicated activity, particularly when products will be used in changing circumstances. The usability of a product is defined by ISO 9241 as the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use. From this definition can be concluded that a product’s usability depends on the situation in which it is used and that this situation should be specified. However, more and more products are used by varying users, for varying purposes and/ or in varying contexts of use, for instance a vending machine or a mobile phone. These types of products therefore have a varying or dynamic usability. This variation can take place on different levels: within a use session, between use sessions or between products. The means by which a product can be adjusted to this variation or ‘dynamic use situation’ depends on the variation level. Products with dynamic use situations are difficult to design with regard to usability because it is difficult - if not impossible - to predict all situations a product will meet. Moreover, requirements from different use situations can conflict. In this paper we will elaborate on the principle of dynamic use situations by means of an example. Furthermore we will discuss the need for the development of a design method that supports designers in dealing with dynamic use situations. For that purpose we propose criteria the method should meet. Besides aiming at creating solutions these criteria include the analysis and prioritizing of use situation aspects as well as an evaluation in which these aspects are integrated. We believe scenarios can be a valuable tool in this process.