A cylindrical test object for use in calibrating an ultrasonic bone analyzer has opposing ends that each contain a transducer seat optimized to allow intimate acoustic contact in spite of mechanical errors such as might be encountered in a scanning system. The test object is made of material having known ultrasonic characteristics. When opposing transducers are placed in the test object transducer seats, the test object is lifted off the holder and is free to rotate and translate over sufficient range to compensate for variances in the relative positions of the transducers. The shapes of the transducer ends and transducer seats are chosen to allow intimate acoustic contact in spite of any such translation or rotation. The test object may be a solid or a liquid encased in a solid.