Final answer:
A pressure gauge measures the pressure of a fluid relative to atmospheric pressure, known as gauge pressure. The gauge reads zero at atmospheric pressure, and positive or negative depending on whether the pressure is above or below this baseline. Different types of gauges, such as an aneroid and manometers, use various mechanisms for measuring pressure.
Step-by-step explanation:
A pressure gauge is a device used to measure the pressure of a fluid. Specifically, gauge pressure is the pressure measured relative to the surrounding atmospheric pressure. It's important to note that gauge pressure is positive when pressures are above atmospheric pressure and negative when pressures are below it.
Most pressure gauges are calibrated to read zero when at atmospheric pressure. This implies that any reading on the gauge indicates the pressure deviation from this baseline. For example, the gauge on a scuba tank measures the pressure inside the tank relative to the atmospheric pressure outside the tank, providing a positive value when the internal pressure exceeds atmospheric pressure.
There are various types of gauges used for pressure measurement. An aneroid gauge, for instance, employs a bellows-and-spring arrangement connected to a pointer that moves over a calibrated scale to indicate pressure levels. On the other hand, devices like manometers utilize the properties of fluids to measure pressure, involving U-shaped tubes and the fluid's density and gravitational force.