[eli5] How does an altimeter work? How does it know how high you are off the ground?
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with planes there is a static port of the outside of the plane that measures the static air around it. that air is channeled into the altimiter housing. in that housing there is also a waifer(think of a balloon) that in mechanically geared to a knob the pilot can twist. that know is also connected to something called the chollsman window.At sea lvl at standard temp the window will be set to 29.92 and the height read on the altimiter would be 0, this is when the air pressure is set in the waifer as well. this can very to a small degree due to humidity as well. when a plane gets weather at their destination airport the collsman window setting is given by the control tower( generally on the atis/awas frequency). once the pilot has the correct setting in their collsman window their altimeter should be within 75 feet of their planes altitude. if you think about air pressure as your go higher the air is thinner letting the waifer expand in the housing. this reads that you have climbed and vise versa as you decend the air becomes thicker and the waifer contracts and shows a decline in the height on the altimeter.
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