Dwyer Series 475 Mark III Handheld Digital Manometer. It measures pressure differences and is used for:
Field calibration of HVAC systems.
Monitoring or troubleshooting HVAC systems.
Clean room inspections.
Air velocity monitoring.
Natural gas appliance-line testing.
It features an accuracy of ±0.5% FS, a rugged aluminum housing, and one-touch calibration technology. It is also FM approved for use with natural gas.