GALAXY Differential Pressure Gauge Dial Size4 inch / 100 mm HVAC Systems The Series G2000 Differential Pressure Gauges are Low-Cost, Diaphragm Operated, Mechanical Pressure Gauges,Series G2000 Are For Measuring Fan And Blower Pressures, Filter Resistance, Furnace Draft, Pressure Drop Across Orifice Plates, Monitoring Blood And Respiratory Pressures In Medical Care Equipment With Simple, Frictionless Movement Parts,It Can Quickly Indicate Low Air Or Non-Corrosive Gas Pressures, Either Positive, Negative or Differential It Can Resist Shock, Vibration and Over-Pressures.