How does an altimeter work? Is an altimeter really just a barometer?
Yes. It is a bellows type barometer. As the bellows expand and contract with air pressure it pushes and pulls a set of gears that rotate the pointer. There is an adjustment that allows the pilot to set the altimeter to the correct altitude. This is done 2 ways: There is a little window that shows atmospheric pressure. The pilot listens to the weather report and sets the pressure shown in the window to the reported pressure. This works even if the airplane is flying. OR While the airplane is on the ground before takeoff, the pilot sets the shown altitude to the known altitude of the airport.
