2004 is a series 2000 MAGNEHELIC® differential pressure gauge. The design resists shock, vibration, over-pressures and is weatherproof to IP67. This simple, frictionless Magnehelic® gauge movement quickly indicates air or noncorrosive gas pressures either positive, negative (vacuum) or differential. Typical applications include filter monitoring, air velocity with Dwyer Pitot tube, blower vacuum monitoring, fan pressure indication, Duct, room or building pressures, clean room positive pressure indication.