1.1 This practice² provides guidelines for measuring the thickness of materials using the contact pulse-echo method at temperatures not to exceed 200°F [93°C].1.2 This practice is applicable to any material in which ultrasonic waves will propagate at a constant velocity throughout the part, and from which back reflections can be obtained and resolved.1.3 The values stated in either inch-pound or SI units are to be regarded as standard. The values given in brackets