There has been a growing interest for studies of group and teams within the research field Human Factors during the last decade. The body of hypoheses and ideas about the team, and especially aspects affecting team performance, is quite extensive. One aspect that is often discussed is that of common ground or shared mental models. However, instrument to capture these aspects are not yet developed. This report is one step towards a solution of that problem. The first part of the report discusses the theoretical underpinnings used, especially psycholinguistic theories. It is further argued that the concept contain at least two important dimensions (calibration and overlap) The presentation of the concept and its dimensions is followed by an example that provides the procedure for a future study. The report also describes how to score and analyze collected data. Finally, the report ends with a discussion about the context and prerequisites that are needed for the instrument to function optimally.