GB/T 37361-2019 "Determination of Paint Film Thickness—Ultrasonic Thickness Gauge Method" is applicable to the measurement of single-layer or multi-layer paint film thickness on hard substrates such as metals and non-metals. It can also be used for quality control and maintenance inspection on coating production lines. Based on the principle of ultrasonic pulse reflection, the ultrasonic thickness gauge emits pulses that penetrate the coating. The thickness is calculated by measuring the round-trip propagation time of the pulses combined with the sound velocity. During measurement, a couplant is required to ensure full contact between the probe and the paint film. The instrument must be regularly calibrated using standard test blocks. The influence of measurement temperature, precision requirements, and the content of the test report should be clearly defined to ensure accurate and reliable measurement results.