Abstract: A calibration standard for an ultrasonic inspection system used to test components having curved surfaces. Several embodiments are disclosed, all having at least one curved surface and a calibration hole providing an internal controlled geometry reflector surface having a body axis which conforms to the curvature of the surface. The several embodiments can be manufactured by several methods, one of which comprises securing a block of electrically conductive material having the desired curved surface in a fixture, placing a moveable electrically conductive electrode adjacent the block to form a gap therebetween, applying a high voltage to the block and the electrode to cause an electrical discharge across the gap while bathing the gap in a dielectric fluid, and advancing the electrode into the interior of the block along a curved path having a center of curvature common to the center of curvature of the curved surface to form an internal bore therein.