Before discussing any attributes for ultrasonic discontinuity size measurement, it is worthwhile to consider the techniques available and the limitations of each. (...)
The second, called beam boundary intercept technique, offers greater advantage in determining both the length and width of most discontinuities of significance. Theoretically, the technique is accurate when used properly. However, the unavoidable variations in probe characteristics plus the requirements for precalibration of equipment and the need for exceptionally skilled personnel somewhat diminish the accuracy of results. Also, the technique becomes more complicated as the thickness of the weld decreases. Regardless of painstaking laborious efforts to minimize the influence, the technique accuracy tolerance on width is seldom better than ± 1/l6 inch (1.6 millimeters).

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