Which device is used to measure pressure below atmospheric pressure?

The device specifically used to measure pressure below atmospheric pressure is a vacuum gauge. Vacuum gauges are designed to monitor negative pressure levels, which occurs when the pressure inside a system is lower than the surrounding atmospheric pressure. This makes them essential in many applications where creating a vacuum is necessary, such as in HVAC systems or laboratory settings.

Vacuum gauges can provide precise readings of how much below atmospheric pressure a system is operating. They are important tools for ensuring systems work efficiently and safely in scenarios where maintaining a specific pressure is critical.

While barometers and manometers are also pressure-measuring instruments, they are typically used for measuring atmospheric pressure or differences in pressure within certain contexts, rather than specifically for below-atmospheric conditions. Pressure gauges can measure various pressures, including those above, at, and below atmospheric pressure, but they may not be optimized for the lower ranges found in vacuum applications. Thus, the vacuum gauge is uniquely suited for this purpose.