What is the distance information provided by DME based on?

DME, or Distance Measuring Equipment, provides pilots with distance information that is based on slant-range distance. This means it measures the straight-line distance from the aircraft to the DME ground station, which takes into account the altitude of the aircraft as well as the horizontal distance to the station.

Since the measurement comes from the aircraft's altitude relative to the ground station’s location, slant-range distance is indeed the most accurate descriptor. This data is critical for navigation, especially when determining how far the aircraft is from a specific point while also considering its altitude.

Other potential answers focus on different types of distances which are less applicable in this context. For example, horizontal distance would only consider the distance over the ground, ignoring altitude. Vertical distance solely addresses the height difference between the two points, while constant ground level distance doesn't accurately describe the measurement technique used by DME. Thus, slant-range distance is the correct and most applicable term for what DME measures.