In this text, we present a complete development with Event-B [1] [2] [3]: a mechanical press. The intention is to show how this can be done in a systematic fashion in order to obtain correct final code. In section 1, we present an informal description of this system. In section 2, we develop two general patterns [4] that we shall subsequently use. The development of these patterns will be made by using the proofs as a mean of discovering the invariants and the guards of the events. In section 3, we define the requirement document in a more precise fashion by using the terminology developed in the definition of the patterns. The main development of the mechanical press will take place in further sections where more design patterns will be presented.