In this paper, a generic model is developed for smart instruments, and SyncCharts of the synchronous model are used to specify automated systems. The generic model provides an external description, which is the user's point of view, and the SyncCharts model gives a behavioral model of the system. From the complementary information offered by these two models of a device, a method to obtain a coherent SyncCharts from a part of the external model is proposed. The classical example of an automobile speed cruise control system is used for illustration.