Dwyer Differential Pressure Digital Manometer Handheld, 475-1-FM, FM Approved, 0-20" w.c. Intrinsically-safe digital manometer for field calibration, monitoring or troubleshooting HVAC systems, performing clean room inspections, air velocity monitoring, and natural gas appliance-line testing FM-approved intrinsically safe for Class 1, Div. 1, Group A, B, C, D, T4 hazardous locations Accuracy is + or - 0.5% of full scale at 60 to 78 degrees F, and + or - 1.5% full scale at 32 to 60 and 78 to 104 degrees F Dual push pads on the front panel control on-off, auto zero, and pressure unit selection between U.S. and metric units Standard connections accept 1/8" or 3/16" inside diameter (ID) vinyl or rubber tubing