1. Vehicle mode: Since the GM200A vehicle model comes with built in data, users cannot perform calibration. In vehicle mode, the coating thickness on iron, aluminum, and zinc substrates can be directly measured, making it suitable for measuring coating thickness on motor vehicles. 2. User mode: In GM200A user mode, users can only measure the coating thickness on a specific metal surface after calibrating the metal substrate, but not other metals. For example, if an iron substrate is calibrated, the coating thickness on an aluminum substrate cannot be measured. 3. Measuring device: The calibration of the GM200A user mode does not affect the vehicle mode. The GM200A vehicle mode is the factory default setting. The factory default setting of the GM200A uses an iron substrate to calibrate the user model. 4. User model calibration: According to the user model calibration requirements, the diameter of the GM200A substrate should be ≥ 50 mm, and the substrate thickness should be ≥ 0.5 mm. The critical thickness of the GM200A for the base metal is ≥ 0.5 mm.