A differential manometer is a device used to measure the pressure difference between two points in a fluid system. It typically consists of a U-shaped tube filled with a liquid, such as water or mercury. The difference in height of the liquid columns in the two arms of the tube indicates the pressure difference, allowing for accurate measurements in various applications. These instruments are commonly used in engineering, HVAC systems, and fluid mechanics to monitor pressure changes. By providing a visual representation of pressure differences, differential manometers help ensure the proper functioning of systems and can assist in diagnosing issues related to fluid flow.