What is the primary purpose of the altimeter?

The primary purpose of the altimeter is to measure the aircraft's altitude above sea level. This instrument is essential for pilots, as it provides crucial information regarding the aircraft's elevation in relation to sea level, which is vital for safe navigation and avoiding terrain and obstacles. By displaying the aircraft's altitude, the altimeter allows pilots to maintain proper flight levels, adhere to air traffic control altitude assignments, and comply with instrument flight rules. Understanding altitude is also critical in ensuring adequate clearance over geographical features and in managing ascent and descent rates during flight operations.