The OVHWizard measures the distance by means of ultrasound and the pulse echo method, i.e. a sonar pulse transmitted by the sensor is reflected by the contact wire and back to the sensor. The time which elapses (runtime) is proportional to the distance. The exact contact wire position is given by the point of intersection of the two distance sensors. The measured data are picked up in synchronisation with the line kilometering, triggered by pulses from a distance sensor.