Pressure measurement fundamentals: A barometer is an instrument that measures which kind of pressure?

Introduction / Context:
Correctly distinguishing absolute, gauge, and differential pressure is essential when selecting instruments and interpreting readings. The classic barometer is one of the earliest pressure-measuring devices and establishes an absolute reference using a vacuum space above a column of fluid (mercury in traditional designs).

Given Data / Assumptions:

• Barometer reading is referenced to a near vacuum (Torricellian vacuum) rather than atmospheric pressure.
• No dynamic (velocity) pressure component is implied.
• Steady ambient conditions are assumed.

Concept / Approach:
Absolute pressure is measured relative to perfect vacuum. A barometer balances atmospheric pressure against a column of liquid in a sealed tube with vacuum above. The height directly reflects the absolute atmospheric pressure. In contrast, gauge pressure instruments (e.g., Bourdon gauges) compare process pressure to the surrounding atmosphere. Dynamic pressure pertains to kinetic energy per unit volume of a moving fluid and is not what a barometer senses.

Step-by-Step Solution:

Verification / Alternative check:
Standard definitions: P_absolute = P_gauge + P_atmospheric. A barometer yields P_atmospheric directly as an absolute value.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming all industrial dials are “gauge” and misclassifying barometric readings; remember the vacuum reference.

Final Answer:
absolute