What type of testing does not allow for the determination of the depth of a discontinuity?

Through transmission testing does not allow for the determination of the depth of a discontinuity because this method relies on measuring the signal that passes through the material from one side to the other. The primary objective of through transmission testing is to detect the presence of discontinuities by observing the reduction in signal amplitude as it passes through the material. Since it evaluates the signal at a specific location on the opposite side of the test piece, it cannot accurately locate or measure how deep a discontinuity might be within the material.

In contrast, other methods, such as angle beam and straight beam testing, can provide information about both the presence and the depth of discontinuities based on the reflection and time of flight of the ultrasonic waves. Surface wave testing primarily focuses on detecting surface-breaking flaws, and while it can give insights into certain types of defects, it is not designed to assess internal discontinuities' depth accurately either.