Calibration apparatus for calibrating an ultrasonic transducer array by moving it along an arcuate calibration test member, includes four upright posts interconnected by a rectangular carriage which is slidably movable vertically along the posts. A horizontal pivot shaft is rotatably mounted on the carriage. Fixed to the shaft and depending therefrom are two pendulum arms, interconnected at their lower ends by a pair of cross bars on which is slidably mounted a mounting block. An attachment rod is vertically slidably movable in the mounting block and carries a coupling joint at its lower end for mounting the transducer array. A reversible gearmotor drives the pivot shaft through a chain and sprocket assembly in an oscillating motion. Backlash in the gear train is reduced by a bias weight.