In general, all ultrasonic systems require calibration prior to their use for screening a product; furthermore, their calibration must be verified frequently. Specially designed calibration standards which contain machined notches simulating actual material defects are used for the calibration of the equipment. Some tolerances must be allowed for machining the simulated defects. When all the tolerances in the ultrasonic system, instrument, sensor, and standards are accumulated, the resulting signal responses are usually less than desired. To maintain the required uniform sensitivity, compensation must be made for these undesirable losses in signal amplitude.