🔍 Key Concepts

• Compound gauge function on machinery and piping systems • Relationship between pressure above atmospheric and below atmospheric (vacuum) • Where on a ship you would see a compound gauge (e.g., suction side of pumps)

💭 Think About

• Which pair of quantities would be useful together on the same dial for monitoring a pump suction line? • Would temperature or humidity normally be combined on the same mechanical gauge with pressure in engine-room piping? • Think about what happens when pressure in a line drops below atmospheric—what does the gauge need to show then?

✅ Before You Answer

• Confirm that a compound gauge is still a type of pressure gauge, not a thermometer or hygrometer • Check which option combines two opposite directions of pressure (above and below atmospheric) • Eliminate any answers that involve quantities usually measured by separate specialized instruments (like thermometers or hygrometers)