A compound pressure gauge is used to measure what?

A compound pressure gauge is designed to measure both positive pressure and vacuum pressure. This type of gauge is particularly useful in systems where the pressure can fluctuate above and below atmospheric pressure. It has a scale that includes both positive and negative values, indicating pressures above and below atmospheric levels, respectively.

For instance, in various applications, there may be scenarios where it becomes necessary to monitor not just the pressure of gases or liquids in a system, but also to determine if any vacuum conditions exist. Vacuum pressure refers to any pressure that is lower than the atmospheric pressure, and the compound gauge efficiently displays this information.

The other types of gauges mentioned in the choices are designed for more specific tasks, making them less versatile than the compound pressure gauge. Therefore, its ability to track both positive and vacuum pressures is what distinguishes it as the correct answer in this context.