Air Pressure Gauge With Dial Size 4 inch / 100 mm are devices that measure the internal pressure of media within a system, are among the most often used instruments in any given industrial facility. Air pressure gauges measure the pressure of air in a pneumatic system. The measurement of air pressure is essential for the proper functioning of many systems and can be used to monitor and control the performance of compressors, pneumatic systems, and other equipment that utilizes air.