This paper summarizes some of the major aspects of precision ultrasonic thickness gauging. Ultrasonic NonDestructive Testing (NDT) characterizing material thickness, integrity, or other physical properties by means of high-frequency sound waves has become a widely used technique for quality control. In thickness gauging, ultrasonic techniques permit quick and reliable measurement of thickness without requiring access to both sides of a part. During the thickness measurement of any corroded plate, the reading of ultrasonic equipment gives many different readings for each time of inspection at same position due to their non uniform surfaces. Due to corrosion of metal piece, a material whose thickness is lower than the low limit of the probe causes measurement errors. Sometimes the displayed reading is twice as big as the actual thickness. To prevent these errors, the critical thin materials should be measured repeatedly for verification. This paper looks at the review causes of poor performance with ultrasonic techniques and suggests some methods to improve the situation.