🔍 Key Concepts

• Bourdon tube gauge operation and what it normally measures • What the word compound usually means when describing a pressure gauge • How pressures below atmospheric are described in engineering

💭 Think About

• Think about what a standard Bourdon tube gauge measures, and then what extra capability a compound version might add. • Which choice is directly related to pressure measurement scales, rather than a completely different physical property? • Consider applications where you need to read both pressure above the atmosphere and pressure below it. What is that below‑atmospheric reading commonly called?

✅ Before You Answer

• Confirm that a standard Bourdon gauge reads pressure relative to atmospheric pressure. • Identify which option refers to a condition of pressure lower than atmospheric, not a different quantity like temperature or humidity. • Make sure the correct choice can logically be placed on the same dial as positive pressure, using the same basic mechanism.