What is a main characteristic of gauge pressure?

Gauge pressure is defined specifically as the pressure relative to atmospheric pressure. This means that it measures the pressure exerted by a fluid in a system above the surrounding atmospheric pressure. When gauge pressure is reported, it indicates how much higher or lower the pressure in a system is compared to atmospheric pressure, which is considered the zero reference point.

For example, if a tire has a gauge pressure of 30 psi, it means the pressure inside the tire is 30 psi greater than atmospheric pressure. This characteristic is crucial in various applications, including HVAC systems, where understanding pressure differences is essential for proper operation and efficiency.

The other options do not accurately represent gauge pressure. For instance, gauge pressure can be zero if the internal pressure matches the atmospheric pressure. It is not inherently negative since it can be zero or positive depending on the system's conditions. Also, gauge pressure is not the same as absolute pressure, which is the total pressure measured from a vacuum (or absolute zero pressure) and includes atmospheric pressure as part of its calculation.