Abstract: An ultrasonic applicator including a parabolic reflector for reflecting ultrasonic beam energy for ultrasonic sectional scanning particularly for medical diagnostic purposes, has its image registering system compensated for the variable sweep velocity of the ultrasonic beam energy within the body region under examination by the provision of a rotary mark carrier with a series of angularly offset marks of variable spacing such that as the mark carrier rotates at a constant rate in synchronism with the rotary ultrasonic transducer head, the marks are scanned at a relatively rapid rate as the ultrasonic impulses are reflected at the border regions of the parabola and are scanned at a progressively slower rate during transducing via points progressively closer to the central region of the parabola.