What component in an altimeter measures the absolute pressure of the air and is usually made of a sealed capsule of corrugated metal?

The correct answer is the aneroid. An aneroid altimeter uses a sealed capsule made of corrugated metal, known as an aneroid barometer, which expands and contracts with changes in atmospheric pressure. As the aircraft ascends or descends, the atmospheric pressure changes, causing the aneroid capsule to move. This movement is mechanically linked to the altimeter's needle, which indicates the altitude on the dial.

This design provides a reliable means to measure absolute air pressure, translating it into altitude readings crucial for navigation and maintaining safe flight levels. The construction and operation of the aneroid capsule allow for accurate and responsive altitude measurements without the need for liquid, which can be found in traditional barometers.