What is the purpose of a U-tube manometer?

A U-tube manometer is primarily used to measure pressure. It consists of a U-shaped tube partially filled with a liquid, typically water or mercury, and is used to gauge the difference in pressure between two points in a system. The height difference of the liquid in the two arms of the manometer is directly related to the pressure difference being measured.

While a U-tube manometer can indicate draft as a specific application of measuring pressure differences in ventilation systems, its broader purpose is to provide an accurate measurement of pressure in various applications, making it a versatile tool for engineers and technicians. In the context of the choices provided, measuring draft is indeed a valid application of a U-tube manometer, but it is not the exclusive purpose, as it is fundamentally designed for measuring pressure.