An absolute manometer is a type of fluid pressure measuring device that measures the absolute pressure of a fluid. Unlike gauge pressure manometers, which measure the difference between the fluid pressure and atmospheric pressure, absolute manometers measure the pressure relative to a perfect vacuum.

Absolute manometers typically consist of a U-tube filled with a liquid that is sealed at both ends, creating a sealed system. One end of the U-tube is connected to the fluid being measured, while the other end is connected to a reference pressure, usually atmospheric pressure. The pressure difference between the two ends of the U-tube is proportional to the absolute pressure of the fluid.

Absolute manometers are commonly used in scientific research, industrial applications, and in measuring the pressure of gases and liquids. They are well suited for measuring absolute pressures in a variety of applications and can be used in a wide range of pressure ranges, from low to high. Absolute manometers are more accurate and repeatable than gauge pressure manometers, but they can be more complex and expensive to use and maintain.