A set of standard reference blocks with the same geometrical configuration and dimensions other than the size of the calibration reflectors, e.g., flat bottom holes, is called a set of:

• A. Distance amplitude standards
• B. Area amplitude standards
• C. Variable frequency blocks
• D. Beam spread measuring blocks

Answer: (B)

Echo amplitude is driven by the size of the reflector when distance, material, and instrument settings are kept constant. Using a set of reference blocks that share the same shape and dimensions but vary only the calibration reflector size (for example flat bottom holes of different diameters) lets you map how the echo strength changes with reflector area. This specific collection is called area amplitude standards, as it focuses on area-driven variations in amplitude to calibrate and verify the system’s response to defects. The other options would involve different variables—distance, frequency, or beam spread—rather than changing reflector area, so they don’t fit this scenario.