The Non-contact Thickness/Displacement Meter is measuring the gap between the target measurement object and the sensor which are facing each other as shown in following figure. At this time, the sensor case and the target measurement object need to be electrically conducted. It is because the electrostatic capacitance is using the electric current to measure the gap. If the impedance (the effective resistance of an electric circuit) between the target measurement object and the sensor is high, it becomes measurement error. Generally, it is within the specification, if the impedance is 1kΩ or less.