Abstract: Apparatus for examining an elongated cylindrical body having an axial bore, such a rotor shaft, which apparatus includes an energy transducer which is supported by a drive rod to be advanced within the bore while obtaining readings indicative of the physical condition of the body, a drive unit supporting the rod, and a fixture for supporting the drive unit in order to center the drive rod within the bore, the fixture being supported by the body and including a mechanism for adjusting the fixture in order to establish the desired axial alignment of the drive rod. The fixture is provided with an arrangement for supporting a calibration block which is used for calibration of the apparatus, the arrangement being adjustable relative to the fixture to bring the calibration block into a desired position relative to the transducer when the drive unit is mounted on the fixture.