Abstract: An ultrasonic ranging device and method for positioning a working implement relative to a datum is disclosed. The ultrasonic ranging device is coupled to the implement and is capable of transmitting an ultrasonic ranging pulse toward the datum and further capable of detecting the occurrence of an echo of the ranging pulse. The ultrasonic ranging device periodically makes a ranging measurement by transmitting an ultrasonic pulse toward the datum and then detecting the occurrence of any echo within a time interval, and repeats this ranging step at a predetermined repetition rate. The ultrasonic ranging device also detects any spurious echoes by detecting the occurrence of an echo within the time interval following no transmission of an ultrasonic pulse. If a spurious echo is detected, then the predetermined repetition rate is changed so that the spurious echo will not interfere with a ranging interval.