A compound gauge is which of the following?

• A. A pressure gauge that can measure positive pressures
• B. A pressure gauge that can measure positive pressures and negative pressures
• C. A temperature gauge
• D. A flow meter

Answer: (B)

A compound gauge is designed to read both positive pressures and vacuum (negative relative to atmospheric pressure). It usually has dual readings: one side shows positive pressure (psig) and the other shows vacuum (often in inches of mercury or a vacuum scale). This lets you know if a system is pressurized or if you’re pulling a vacuum, which is essential in refrigeration and HVAC service. It isn’t a temperature gauge or a flow meter, which measure temperature or flow rate, respectively.