A manometer is an instrument used to measure and indicate pressure. There are two types of manometers, analog and digital. The most basic and simplest form of an analog is the U-Tube manometer, a glass or rubber tube bent in the shape of a “U” where numbers are listed and spaced every inch on each side, and water is placed in between the bends of the “U”. When pressure is applied, either positively or negatively, the water moves to indicate the pressure behind it expressed in inches of water column (inWC). Inches of water column is the most common form of measurement in the HVAC industry when measuring static or gas pressure, although other units of measure are available and used worldwide.