Product development is a complex process based on problem solving. Problem analysis attempts to find the best possible solution, but each solution may create new problems. Design rationale is a documentation of a decision-making process so that the decisions made can be reviewed at any time in the future. One of the most common problem-based methods is the IBIS (Issue-Based Information Systems). IBIS diagrams place the problem in the center of the observation, which branches out into possible solutions, which each have pro and con arguments. The diagrams where created using designVUE, an open source software developed at Imperial College London. The thesis was based on a project for the development of a non-destructive testing device in company INETEC for the ITER (International Thermonuclear Experimental Reactor). The device was developed by a small multidisciplinary team in collaboration with multiple associates. Amongst the problem that arose, only the most varied where selected to demonstrate the benefits of the IBIS method and the capabilities of the designVUE software. For the selected problems, the diagrams where created and hierarchically structured. The diagrams are interconnected to show the relationship between the problems and the product development pathway. Characteristic problems where highlighted such as: initial, isolated, coupled and interaction problems. Guidelines for incorporating diagrams in technical documentation where given, with the emphasis on preserving links in text documents. Finally, an example of further data storing is given, in which all decision-makers regularly record knowledge and decision.