What Does an Altimeter Do?

An altimeter is a device that measures altitude—a location's distance above sea level. Most altimeters are barometric, meaning they measure altitude by calculating the location's air pressure. Air pressure decreases as altitude increases.

How does altimeter work?

The altimeter measures the height of an aircraft above a fixed level. The instrument senses this by taking the ambient air pressure from the static port. ... As the aircraft goes up, the pressure inside the case decreases and the bellows expand. The opposite happens as the aircraft descends.

What happens when you change altimeter setting?

When you adjust the altimeter setting to a higher barometric pressure (29.92 to 30.02, for instance), your altimeter indication moves upwards (from, say, 5000 feet to 5100 feet). On the altimeter, increase in setting (pressure) means an increase in altitude.