The internal structure of old musical instruments is of great interest to musicians, restorers, and instrument makers. As part of the MUSICES project, Fraunhofer researchers are using 3-D computed tomography methods to examine historical musical instruments belonging to the collection held by the Germanisches Nationalmuseum (GNM). Based on this experience, they are drawing up guidelines for obtaining the best possible images and measurement results. Until now, there has been no standard for such measurements. The results of the project will be published online.