Which measurement provides the best information on the progress of a flight between two enroute waypoints from RNAV equipment?

The measurement that provides the best information on the progress of a flight between two enroute waypoints from RNAV equipment is the Estimated Time Overhead (ETO). ETO refers to the calculated time at which an aircraft is expected to reach a specific waypoint. It is particularly useful for assessing the progress of the flight in real-time, enabling pilots and flight planners to track and optimize their flight path effectively.

Using ETO allows for immediate adjustments if necessary, based on current flying conditions or any deviations from the planned route. This metric takes into account the aircraft's ground speed and can be regularly updated as the flight progresses, making it a dynamic measurement that reflects the real-time situation more accurately than others.

Other options like Elapsed Time on Route provide a historical perspective on how long the flight has been underway but do not specifically relate to the anticipated time over a forthcoming waypoint. Estimated Time of Departure might imply when a flight will start but lacks relevance to assessing the progress during flight. Actual Time of Arrival gives a post-flight metric, which does not assist pilots in-flight when they need timely and relevant information about their current progress towards their next waypoint. Therefore, ETO serves as the most practical and effective measurement in this context.