Temporal Reliability of Estimates from Contingent Valuation

A scanning unit for moving an ultrasonic wave transmitting/receiving head has means for moving the head linearly and means for swinging the head so that a series of linear scans can be performed with the head swung at differing angles for each scan. Utilization of the received signals may be to give a "B-scan" presentation on a bi-stable storage tube. The unit is preferable immersible in water and has one important application for the ultrasonic inspection of nuclear reactor pressure vessels.