What information does an altimeter provide in an aircraft?

An altimeter is a crucial instrument in aviation that measures the aircraft's altitude above sea level. It functions by detecting changes in atmospheric pressure—the higher an aircraft climbs, the lower the air pressure it encounters. By translating this pressure data into altitude readings, the altimeter enables pilots to understand their vertical position relative to sea level. This information is vital for safety, navigation, and flight operations, as it ensures that the aircraft maintains appropriate altitude to avoid obstacles and adhere to air traffic regulations.

Other options pertain to different aspects of flight or aircraft performance, but they are not the functions of an altimeter. For instance, an altimeter does not measure the aircraft's speed, fuel consumption, or weather conditions. Each of these metrics is monitored by other specialized instruments and systems in the cockpit. Therefore, the primary role of an altimeter specifically relates to providing altitude information, making the correct option clear.