In atomic and thermal power engineering, welded joints from 5.5 and 2.0 mm thick, respectively, are inspected by ultrasonic testing. For thicknesses up to 20 mm, instruments are tuned by reference blocks containing angle reflectors (notches). For thicknesses more than 20 mm, AVG diagrams are used for tuning instruments and evaluating the quality of the tested welded joints (AVG and DGS are families of curves for different diameters of flat-bottom reflectors plotted in the coordinates distance (X) and gain (Y); the analogue in Russian documents is DGS diagrams).