What is the basic procedure for a simple straight-beam thickness measurement in a plate?

• A. Apply a normal incidence probe with known velocity; measure time-of-flight to back wall; calculate thickness using thickness = c × t / 2; and verify with a reference block.
• B. Apply a oblique incidence and measure impedance.
• C. Use a contact method with unknown velocity.
• D. Use a calibration block only.

Answer: (A)