A post hoc analysis of data collected from a usability test on the Fluke ScopeMeter 97 (a diagnostic instrument for analyzing electrical signals) revealed that, in doing tasks, subjects were making use of their own internal metaphors (user generated) that were unsupported by the design of the ScopeMeter keys. We investigated the interaction of the user generated metaphors and designer generated metaphors. By examining the effects that the subjects' skill levels and their backgrounds had on employing such metaphors, we began to outline certain characteristics of user generated metaphors. We found that user generated metaphors demonstrate unyielding persistence in the minds of ScopeMeter users, particularly in the higher skilled subjects.