Abstract: Apparatus (10) for performing ultrasonic flaw testing of a material (M) or assembly. A pulser (28) generates an electrical pulse having defined characteristics. A transducer (12) converts the signal to an ultrasonic pulse, propagates the pulse through the material or assembly, receives an echo the characteristics of which include reflections off flaws or discontinuities in the material or assembly, and converts the echo into an electrical reply signal. The transducer is selectable from among a number of transducers. A processor (32) processes the reply signal to produce a visual display representing the amplitude of the reply signal for a range of propagation times (distances) into the material. A visual display (16) displays the processed electrical signal. A correlation module (42) generates a gate signal which is visually displayed (at 38) with the processed electrical signal. The gate signal corresponds to a maximum amplitude value which represents the maximum flaw size allowable for the test.