Definition
An instrument at an air traffic control facility that displays the current local barometric pressure, corrected to sea level, which controllers pass to pilots so they can set their aircraft altimeters to read accurate altitudes.
Plain English
A small pressure gauge in the control tower or weather office that shows the current local pressure setting. Controllers read this number to pilots so the pilots can adjust their altimeters and get correct altitude readings.
Context Anchor
Seen on the face of a pressure altimeter when setting the altimeter before takeoff, during flight, or before landing.
Derivation
Altimeter comes from Latin roots meaning “height” and “measure.” Indicator comes from a Latin word meaning “to point out.” Together, the term means the part of the height-measuring instrument that points out which pressure setting is being used.
Why Pilots Care
Using the correct altimeter setting prevents altitude errors that could lead to terrain conflicts or airspace violations.
Intuition Check
Do not confuse the altimeter setting indicator with the altitude pointers. The altitude pointers show altitude; the altimeter setting indicator shows the pressure setting used to make that altitude reading correct.
Example Sentence 1
The tower controller checked the altimeter setting indicator and reported the current setting as 30.05.
Example Sentence 2
The FSS briefer confirmed the altimeter setting indicator value matched the current METAR.