The estimated time of arrival or ETA (sometimes called ETOA) is a measure of when a ship, vehicle, aircraft, cargo, emergency service or computer file is expected to arrive at a certain place. One of the more common uses is in public transportation where the movements of trains, buses, airplanes and the like can be used to generate estimated times of arrival depending on either a static timetable or through measurements on traffic intensity. In this respect, the phrase or its abbreviation is often paired with its complement, "estimated time of departure" or "ETD", to indicate the expected start time of a particular journey. This information is often conveyed to a passenger information system as part of the core functionality of intelligent transportation systems. For example, a certain flight may have a calculated ETA based on the speed by which it has covered the distance traveled so far. The remaining distance is divided by the speed previously measured to roughly estimate the arrival time. This particular method does not take into account any unexpected events (such as new wind directions) which may occur on the way to the flight's destination. ETA is also used metaphorically in situations where nothing actually moves physically, as in describing the time estimated for a certain task to complete (e.g. work undertaken by an individual; a computation undertaken by a computer program; or a process undertaken by an organization). The associated term is "estimated time of accomplishment", which may be a backronym. For example, Bittorrent clients specify ETA as the expected time remaining for a file to completely download as 1d4h (1 day and 4 hours), 1w2d (1 week and 2 days), etc.

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