Laraine Landon, age 12, of Vernal, UT for her  question:

How does an airplane altimeter work?

The altimeter in an airplane is a special barometer, an instrument for measuring the pressure of the air. By and large, the higher we go, the less air there is above us and the lighter it weighs, The altimeter is a highly refined instrument for measuring height in terms of air pressure.

As we know, the pressure of the air at any point on the earth varies with every change in the weather and with every wind that blows. This means that a pilot's altimeter is in constant need of adjustment. As he flies over one contact point after another, the pilot is given air pressure conditions on the ground. He constantly corrects his altimeter in line with this information and the refined barometer gives him his height in feet.