What does a pressure gauge indicate?

A pressure gauge specifically measures the pressure of a gas or liquid within a system, expressing how much force the fluid exerts against the walls of its container. This measurement is commonly compared to atmospheric pressure, which allows for a clear understanding of the fluid's pressure relative to the surrounding environment. Pressure gauges are essential for monitoring the performance of systems in various engineering applications, including hydraulics and pneumatics, to ensure safe and efficient operation.

The other options are distinct measurements that do not pertain to what a pressure gauge indicates. For instance, temperature is measured by a thermometer, flow rate is determined using flow meters, and viscosity refers to a fluid's resistance to flow and is assessed using viscometers. Each of these parameters provides valuable information, but they operate completely independently from the measurement of pressure.