Manometer measurement principle A standard U-tube or differential manometer is primarily used to indicate which form of pressure?

Introduction / Context:
Manometers are foundational instruments in fluid mechanics labs and process plants. They balance a column of fluid against an applied pressure, letting us compare an unknown pressure to a known reference, most commonly the ambient atmosphere.

Given Data / Assumptions:

• Instrument: U-tube or differential manometer.
• Reference leg often open to atmosphere.
• Working fluid: mercury, water, or manometer oil.

Concept / Approach:
A manometer indicates pressure relative to its reference leg. If the reference is the atmosphere (open leg), the reading is pressure above or below atmospheric pressure — i.e., gauge pressure. Absolute pressure requires an absolute reference (perfect vacuum) as in a barometer; differential pressure uses two process taps.

Step-by-Step Solution:

Verification / Alternative check:
In a barometer, one side is vacuum, so it reads absolute atmospheric pressure. In contrast, a process manometer against atmosphere reads gauge pressure by definition.

Why Other Options Are Wrong:

Common Pitfalls:
Treating all column devices as “absolute.” The reference connection defines whether the indication is gauge, differential, or absolute.

Final Answer:
gauge