A device for using electromagnetic pulses to determine a distance to a surface includes a pulse generator, a real time sampler and a calibration unit having a signal generator for generating a calibration signal with a predefined frequency. In a calibration mode the real time sampler receives the calibration signal, and an average sample time delay of the sampler is determined based on the sampled calibration signal and the known calibration frequency. In a measurement mode, the real time sampler receives a reflection signal and the distance is determined based on a sampled reflection signal and the average sample time delay. Knowledge of the average delay of the sampler makes it possible to exactly determine the distance (in time and thus space) between two points in the sampled signal.