Wheelchair speed control can be done using a state machine with fixed speed per event [Fig. 4(b)] or proportional speed to state vector. The easier guidance option consists on commands mutually exclusive and speed fixed per event. Note that a fixed speed per event is assigned, the maximum gradient and values of the linear and angular speeds of the wheelchair have to be customized for each user. Another option consists on using proportional speed to state vector. In this way, selecting FORWARD or BACKWARD commands, the linear speed is fixed in each moment, and with RIGHT and LEFT commands the angular speed is fixed. This allows us to make continuous control of the wheelchair. Nevertheless, this type of guidance requires a great precision by the user, and we must keep in mind that small shifts between interface and head position or head movements cause a displacement of the cursor in the screen very difficult to avoid and correct.