A methodology is described which is designed to support user-centred design of computer-based systems. The main concern is for a specific consequence of the design of computer-based systems, the procedural, device-specific knowledge required from the operator. The objective is to raise the efficiency of work by adapting the functional design of the device to the task requirements. The method is based on the formal language SL/R for the modelling of procedural knowledge and includes separate models of device functions and task requirements. Evaluation is based on simulated user procedures and should help to identify design deficiencies. Other application areas are the development of user support for defined tasks and systems.