"The display of continuous and temporal exhibitions should be organized with regard to efficient dissemination of background ideas and intended messages towards an interested public. In most cases this public is not known in advance, neither in its quantity nor in its structure. In order to get information, whether the general demand and special issues are or are not performed by the realized exhibition, it is necessary to define operational goals and make explicit statements on its contents. With the help of a inventory like this it is possible, not only to measure the "success" of an exhibition by comparing the number of visitors with those expected to come, but to carry out "sum mative evaluation" of the distribution of learning effects among the public. It is important to stress the fact, that the outcome of all surveys of this type has the form of "data-distributions", with partially contradictory tendencies. This is because of the heterogenity of visitors, their individual predispositions and selective perception, the different meaning exhibits present to different people etc. Therefore it is quite normal, to expect a considerable gap between intentions, layout and presentation structures on the one hand and preferences, capacities of understanding and interest of the target groups on the other. In order to adapt concept, design and didactic means to the latter - which in most cases is a question of finding acceptable compromises - it is useful and sometimes necessary to get the information about the "gaps" and their causes already before furnishing the final exhibition display. Therefore, "formative evaluation" with the help of mock-up environments has proved to be an instructive step bringing feed-back on the consequences of alternative exhibitional versions into the planning process. If there is already an existing presentation to be improved or modernized, it is helpful to start with a status quo evaluation in order to analyze its most serious shortcomings and weak points. The contribution to present will describe experience in different types of museums with these approaches, the difficulties to establish this kind of empirical research and to integrate it into the planning and designing process and will try to illustrate pitfalls and benefits of the method for museums and visitors."