What is the proper definition of an altimeter setting?

• A. Station pressure corrected for height of the station above sea level.
• B. The altimeter's default at sea level.
• C. A setting that adjusts for outside air temperature variations.
• D. A calibration constant for instrument error.

Answer: (A)

The essential idea is that the altimeter setting is the sea-level pressure value derived from what the atmosphere is doing at your location, adjusted for the station’s elevation. You take the pressure you measure at the station and convert it to the pressure that would exist at sea level if you were at that same location. That sea-level pressure is what you dial into the altimeter. With that setting, the altimeter indicates your altitude above mean sea level, not the height above the terrain.

So this definition matches the idea of “station pressure corrected for height of the station above sea level.” It isn’t a fixed default, it isn’t correcting for temperature variations, and it isn’t a calibration constant for instrument error.