Dwyer Magnehelic gage for high accuracy, guaranteed within 2% of full scale and for the wide choice of 81 models available to suit your needs precisely. Using Dwyer's simple, frictionless Magnehelic gage movement, it quickly indicates low air or noncorrosive gas pressures, either positive, negative (vacuum) or differential. The design resists shock, vibration and over-pressures. No manometer fluid to evaporate, freeze or cause toxic or leveling problems.