[Ryan F.]

Originally Posted by KenWittlief

in fact, when you are flying it is impossible to measure your ground speed, unless you know the wind speed and direction. Aircraft do not have speedometers attached to their wheels :^)

In jumps a beautiful aircraft device we like to call theDME .

Watches your change in distance from a VOR point, and gives you your airspeed. It only works when the pilot is flying directly too or from the VOR (though that is fairly common).