During the last decade, major changes have been occurring in the NDE industry. Driven by advances in structural design, maintenance, and life extension practices, a new emphasis on the quantitative interpretation of nondestructive measurements has emerged (1-3). It is no longer practical to overdesign a system to accommodate the wide range of flaw sizes that might be accepted by a qualitative inspection. Instead, the cost, safety, and performance requirements of many major systems can only be attained by maximizing (and specifying) the reliability of flaw detection, by making quantitative estimates of the sizes of the detected flaws, and by measuring material properties and environmental conditions which influence the rate of flaw growth and the load at which catastrophic failure is expected to occur.