When is pressure measured without considering the current atmospheric pressure?

Pressure is measured without considering the current atmospheric pressure in the case of absolute pressure. Absolute pressure is defined as the total pressure exerted by a system, including both the atmospheric pressure and the pressure of the gas or liquid in the system. Consequently, it is measured relative to a perfect vacuum, where zero pressure exists.

In practical terms, absolute pressure gives a clearer understanding of how a system behaves under varying conditions and is essential in scientific calculations, especially in thermodynamics and fluid dynamics. This measurement is critical when working with HVAC systems and refrigeration cycles, as it enables technicians to calculate correct operating pressures and determine system performance without the variability introduced by atmospheric pressure.

In contrast, gauge pressure measures the pressure relative to the atmospheric pressure, meaning it can be influenced by changes in the weather or altitude. Vacuum pressure refers specifically to pressures that fall below atmospheric pressure, and relative pressure is often used interchangeably with gauge pressure as well. Therefore, the measurement of absolute pressure stands out as it provides a consistent reference point unaffected by external atmospheric conditions.