[en] The proposed ultrasonic measuring instrument has a generator for pulsed ultrasonic signals, a detector as well as a contact arrangement that connects both with the work piece. The transportation lag of the signals through the contact arrangements amounts to at least five times the transportation lag of the signals due to the thickness of a work piece. Furthermore there is an arrangement for the measurement of the delay between two successive echos from the back of the work piece with the help of a zero passage detector for the generation of a time-reference value on each echo signal. This permits an exact time control of the pulses which range in the field around nano seconds. The instrument is explained with 8 drawings and a detailed description. (RW)