The Dwyer 2001AV Magnehelic Differential Pressure Gauge, Dual Scale, 0-1.0" w.c., 500-4000 FPM for high accuracy and with a dual W.C. and Air Velocity scale that has an accuracy within 2%. Using Dwyer's simple, frictionless Magnehelic gauge movement, it quickly indicates low air or non-corrosive gas pressures; either positive, negative (vacuum) or differential. The design resists shock, vibration and over-pressures. The 2001AV has a dual scale range of 0 - 1.0" w.c. and 500-4000 velocity FPM.