Barometric Altimeter

A barometric altimeter consists of a barometric capsule linked to a pointer by a suitable mechanical or electronic system. The pointer moves across the dial in response to changes in barometric pressure. The dial is calibrated in feet, or (less commonly) in metres.
Barometric altimeters are provided with a pressure setting control and sub-scale (Kollsman window) so that the altimeter may be calibrated according to the appropriate pressure setting to indicate flight level, altitude above mean sea level, or altitude above ground level.
The altimeter provides an output to the transponder system to enable the transmission of the flight level or altitude to the air traffic control.

Sources:

A dictionary of Aviation, (1973) Wragg, David W. Retrieved from: http://surl.li/pzpzt

Altimeter. (2024). Basic Air Data. Retrieved from: http://surl.li/pviyi

Altimeter. (2021-2024). SKYbrary. Aviation safety. Retrieved from: http://surl.li/pvixa