What is the function of an altimeter?

An altimeter functions by measuring altitude through changes in air pressure. As altitude increases, the air pressure decreases, allowing the altimeter to calculate the elevation above sea level based on these pressure changes. This makes the altimeter an essential instrument for pilots, hikers, and meteorologists who need to know the height at which they are operating.

The other options relate to different atmospheric measurements, such as temperature, wind speed, and humidity, which are not the purpose of an altimeter. Each of those measurements requires specific instruments designed to capture and interpret the relevant data, but none of them relate to determining altitude based on atmospheric pressure changes.