The terms used, such as control, control task and software quality, are explained in detail so that the terms can be used clearly. The problems of control design are discussed in the basic procedure and presented in a process flow. Due to the introduction of state-zone modelling (SZM), the control process must be extended to include the modelling of the human-machine interface (HMI). Based on a practical example, known methods for modelling the control task are applied. State-zone modelling is introduced and then contrasted with common models and discussed.