The Dwyer Series 477 intrinsically-safe digital manometer provides positive, negative, and differential pressure measurements, and is used to perform field calibration, monitoring or troubleshooting HVAC systems, performing clean room inspections, air velocity monitoring, and natural gas appliance-line testing. The meter is FM-approved intrinsically safe for Class 1, Div. 1, Group A, B, C, D, T4 hazardous locations. It has an accuracy of + 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. The extruded aluminum case provides durability. The backlit four-digit LCD displays the pressure measurement. User-selectable measurement units include inH2O, mmH2O, bar, mbar, psi, inHg, mmHg, Pa, and kPa. The non-volatile memory function provides storage of up to 40 readings, and audible and visual alarms indicate out-of-range measurements. The zero function nulls minor pressure differences before measuring, and display hold retains last reading when the display cannot be seen during testing. The meter is powered by a 9V battery (included) and automatically shuts off after 20 minutes to preserve battery life.

H is height, the vertical distance from the lowest to highest point; W is width, the horizontal distance from left to right; D is depth, the horizontal distance from front to back.

Manometers measure the pressure of a liquid or gas. They are used in laboratory, medical equipment, engineering, automotive, and heating, ventilation, and air-conditioning applications. Manometers measure any combination of gauge, absolute, or differential pressures. Gauge pressure is the amount of pressure in a system relative to the ambient pressure, absolute pressure is the amount of pressure in a system relative to an absolute vacuum, and differential pressure is the difference between two pressures. Analog manometers are composed of columns of liquid, and they use gravity and the liquid's density to calculate pressure. Because they have no moving parts, analog manometers do not require re-calibration. Digital manometers have pressure sensors that are connected to a system with a hose to provide a digital readout of the amount of pressure present in a system. They use microprocessors to calculate pressure, and they require periodic calibration to help ensure accuracy.

Dwyer Instruments manufactures measurement and control instruments, including pressure gauges, flow meters, level instrumentation, temperature instrumentation, and air quality monitors. The company, founded in 1931, is headquartered in Michigan City, IN.