The reproducibility of the ultrasonic response of aluminum calibration blocks, as defined in ASTM standard E-127 [1,2] is of considerable interest because of the use of these blocks as calibration and reference standards. However, there is a general perception that the ultrasonic attenuation in the materials from which these blocks are produced has changed with time, a consequence of the evolution of the metallurgical processing procedures used to produce the rolled rod from which the standards are fabricated. Among the issues that this raises are questions concerning the influence of E-127 block attenuation on the sizing of flaws in materials produced by other processes, e.g., rolled plate, and whether standards should be alloy specific.