Abstract: A reference standard for calibrating ultrasonic flaw detection test equipment and the like. The standard comprises a substantially solid body having at least one surface adapted to be engaged by the test equipment and a void of known dimensions located within the body at a known distance from the test equipment engaging surface. The standard may be constructed of two or more substantially solid bodies, at least one of which contains an aperture of known dimensions, and at least one of which is of known length and contains a surface adapted to be engaged by the test equipment, the bodies being diffusion bonded together to substantially eliminate the bond line such that the aperture forms a void of known dimensions within the substantially solid body at a known distance from the equipment engaging surface. In one embodiment, test equipment may be dynamically calibrated by rotating the standard about its longitudinal axis to produce a dynamic calibrated signal.