What does the DME measure in order to provide distance information?

DME, or Distance Measuring Equipment, operates by measuring the time it takes for a radio signal to travel from the aircraft to a ground-based DME station and back. When the aircraft transmits a signal to the DME station, the station responds with a return signal. The DME then calculates the distance based on the elapsed time between sending the initial signal and receiving the echoed response. Since radio waves travel at the speed of light, the time measurement can be translated into a distance figure, thus providing the pilot with accurate distance information to the DME station.

The other options don't pertain to the function of DME. The angle of ascent does not influence distance measurement, as DME is solely focused on the direct distance based on time. Similarly, while the speed of the aircraft could affect travel time to a destination, it does not play a role in how DME calculates distance. Wind speed and direction also do not factor into the function of DME, which only concerns itself with timing and signal propagation.