Ultrasonic thickness gauges are designed to measure thickness of materials from one side using ultrasonic sound waves. When an ultrasonic wave is sent through the material, this signal is reflected by the back wall of the material and received by the wall thickness gauge. The delay between sending and receiving the signal can be used to calculate the wall thickness of the material. Common applications where ultrasonic thickness gauges are used are measuring corrosion on ship hulls or inside pipes from the outside. Other common applications are measurement of wall thickness of plastic and glass bottles and metal cans or containers. Ultrasonic thickness gauges can be used for all kinds of quality control or inspection purposes. Measurements at height can be dangerous, expensive, and time-consuming. When possible, working at heights should be eliminated. Studies have proven that there is no statistical difference between the data gathered by a Ultrasonic thickness device in a human hand and a Ultrasonic thickness device mounted on an drone.