Dwyer 1235 series well-tube type manometer uses red gauge fluid, or mercury or green color concentrate to provide direct reading of positive, negative, and differential pressure measurement for determining velocity and static pressures, leakage, fan and blower efficiency, filter resistance, and gas pressures. The manometer is calibrated in inH2O or mmH2O using water and is available in W/M-style for use with fluorescein green concentrate or mercury (sold separately), or D-style for use with red gauge fluid. The water column has 1/10" divisions for inch scales or 2mm for metric units. The scales have a positive mechanism to speed adjustments. Units are silkscreened in black on a white background to ease reading, and sealed with mylar to resist wear. Well assemblies are machined from solid acrylic plastic for durability and are permanently bonded to shatterproof clear plastic tubing to provide leak-proof joints. Visible wells and glands allow operators to inspect the manometer, and overpressure traps prevent fluid loss. The manometer has magnetic clips to mount on vertical surfaces and a clamp bar to prevent slipping. Magnets are removable to customize mounting.

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.