Model SDMN6 Dual Port Manometer and Pressure Switch Tester measures gas and static pressure and accurately tests pressure switches by simulating a draft with an internal pump. The instrument tests the pressure switch to determine if it is working properly or if it is starting to fail, which can cause the furnace to run in an unsafe manner. The dual-port manometer can determine if the gas pressure coming into the house or out of the regulator is correct. It measures gas pressure up to 60 inches water column (wc) with a resolution of 0.1 inch wc. The unit measures both positive and negative pressure, which is used for measurement on vacuum control lines. It will take differential pressure readings and display the difference between P1 and P2 at all times in the lower right corner of the easy-to-read LCD. Four different measurement scales can be used: inches of water column, millimeters of water column, mBar, and pounds per square inch.