What does altimeter mean?
Altimeter indicates altitude of air craft from ground. they are known as radio altimeters.
In order to answer your question, first I will briefly explain how an altimeter works. An altimeter senses current atmospheric pressure, and converts it into an altitude reading. The lower the pressure, the higher altitude it will show. In aviation, the pilot needs to select the correct altimeter setting before takeoff and during flight in order to get a correct reading. This is required because the pressure at sea level changes based on weather conditions…
An altimeter determines the height by the difference in air pressure. The higher you go the thinner the air becomes (lower air pressure). A skydiver will zero his altimeter on the ground, and as the skydiver increases altitude the altimeter can determine the distance traveled by determining the difference in air pressure.