Abstract: Method and apparatus for maintaining parallel relationship between the working face of a sound transducer and a planar surface of a workpiece or object under examination by the transducer, and for measuring and adjusting the thickness of a layer of liquid located between the transducer and object. A calibrating method and circuit is also associated with the transducer. Included is the step of placing the working face of the transducer in a position that is adjacent to but spaced from a front planar surface of the object, and providing the layer of liquid between the two. The transducer is then energized such that sound energy is directed into and reflected from the object after passing through the layer of liquid, the sound energy reflected from the object being received at the working face of the transducer.