The position and orientation of a mobile unit is determined from ultrasonic waves received from beacons of known location. The probe can contact multiple electrically conductive elements inside the pad and thereby electrically connect to the pad at multiple locations inside the pad. The deck and compartment lids together define a substantially flat surface that is covered by a vehicle carpet. The optical element is arranged andor embodied in such a way that the field of vision of the camera system has a maximum viewing angle alpha of at least 120\xb0, preferably at least 150\xb0, and especially at least 180\xb0, in at least one plane which is coplanar to the direction of observation of the camera system. It is proposed that, during a time period a setpoint fuel quantity is varied individually for each cylinder in such a way that the average formed over the time period equals, at least approximately, a normal setpoint fuel quantity which would have to be injected without the above-mentioned variation for inducing or maintaining a setpoint operating state of the internal combustion engine. Then, comparing those median horizontal positions from a current image frame to the representative horizontal positions from a previous image frame to determine a change in the patient’s position.