Which device uses a liquid column to measure vacuum?

A manometer is specifically designed to measure pressure differences by utilizing a liquid column, making it well-suited for measuring vacuum. When measuring vacuum, the pressure inside a system is lower than the atmospheric pressure outside. The manometer reflects this difference using a liquid, typically mercury or water, where the height of the column indicates the level of vacuum being measured.

This functionality is different from the other devices listed. A Bourdon tube, for example, is used to measure pressure but lacks the liquid column mechanism utilized in manometers. Pressure gauges may also measure pressure levels but typically use different technologies, such as diaphragm or Bourdon tube mechanisms, rather than a liquid column. Similarly, bellows devices are designed for measuring varying pressures through mechanical movement, not through liquid columns. Therefore, the use of a liquid column uniquely defines the operation of a manometer in measuring vacuum conditions.