Some of the problems with process measurement are generally due to the fact that the definition of measurement plans does not rely on a reference model of the development process that can drive and explain the measuring activities. One of the most popular methodologies addressing the definition of process measurement plans is the GQM (Goal/Question/Metrics). This paper discusses how to support the creation of GQM plans by means of an explicit model of the process being measured. Such a model guides the GQM process, and makes it possible to define precisely –if not formally– the metrics involved. A tool supporting the proposed method is also illustrated.