Definition 1 of 2
Definition
An instrument that measures atmospheric pressure. Common types include the mercury barometer, which balances a column of mercury against the weight of the atmosphere, and the aneroid barometer, which uses a sealed metal capsule that flexes as outside pressure changes.
Plain English
A device that measures how heavily the air is pressing down at a given location and time.
Context Anchor
Seen in weather reports, altimeter-setting discussions, and basic aircraft instrument training.
Derivation
From the Greek baros meaning 'weight' and metron meaning 'measure' -- literally 'weight measurer.' That fits because a barometer is measuring the weight of the air column above it.
Why Pilots Care
Correct barometer readings let pilots set altimeters accurately so they know their true altitude.
Grounding Statement
If air pressure is higher or lower than expected, a pressure-based instrument can give a misleading reading unless it is set correctly.
Intuition Check
A barometer does not measure altitude directly. It measures air pressure, which pilots can use with other information to set or interpret certain instruments.
Example Sentence 1
The barometer at the field showed 30.05 inches of mercury, so the pilot set that value in the altimeter before takeoff.
Example Sentence 2
A steadily falling barometer warned of an approaching low-pressure weather system.