The meters are called "Non-contact displacement meter" or "Thickness meter", and detect physical quantity, such as displacement, vibration, and thickness, with non-contact probes, then convert to electrical quantity and measure original physical quantity accurately. The sensor that is integrated inside the probes detects the quantity. The methods are capacitance, laser (heterodyne, interference), fiber optics etc. As every method has its own characteristics, you can choose its usage. As measurements are performed using a non-contact method, you can measure accurately without affecting the object being tested.
Demands on the non-contact displacement meter have grown vastly in recent years, such as semiconductors, precision motors, various disks (such as hard disks and compact disks, etc), and various films, and both meters have had to expand to meet those needs.