The ultrasonic pulse-echo overlap method is modified to permit automatic recording of the ultrasonic round trip time. A transient recorder is used to capture selected echoes in the echo train. The circuitry used to select the correct trigger pulses for the transient recorder is controlled by the computer. If the transient recorder is triggered with a time interval equal to round trip time or to a fraction of that rate, then there is a perfect correlation between the captured echoes. The value of the correlation is used to generate a control voltage. There is no real limitation on the dynamic range of the system. Results are presented confirming that controllability is within +or-3 ns.