Final answer:
The primary difference between pressure and vacuum gauges is that pressure gauges measure pressures above atmospheric pressure, indicating positive values, while vacuum gauges measure below atmospheric pressure, indicating negative values. Aneroid gauges and manometers are common tools for these measurements with the former used for pressures and the latter potentially for vacuums.
Step-by-step explanation:
The main differences between a pressure gauge and a vacuum gauge lie in the type of pressure they measure and how they are calibrated. A pressure gauge measures pressure that is above the atmospheric pressure, known as gauge pressure. This type of gauge will often read zero at atmospheric pressure and provides positive values when the pressure is higher than atmospheric pressure. In contrast, a vacuum gauge is designed to measure pressures that are below atmospheric pressure. It is calibrated to read negative values when the pressure is less than the atmospheric pressure.
An example of a pressure measuring device is an aneroid gauge, which uses a bellows-and-spring arrangement to move a pointer along a calibrated scale, indicating the pressure level. For measuring very low pressures such as vacuums, open-tube manometers with U-shaped tubes are commonly used, as they can indicate the difference in mercury levels, which corresponds to the pressure level.
The term absolute pressure is used to describe the sum of gauge pressure and atmospheric pressure, providing a measurement from an absolute vacuum reference. Barometers and manometers are also related devices; barometers measure atmospheric pressure, whereas manometers can measure the pressure of contained gases within an apparatus.