The term "pulldown" comes from the mechanical process of "pulling" (physically moving) the film downward within the film portion of the transport mechanism, to advance it from one frame to the next at a repetitive rate (nominally 24 frames/s). This is accomplished in two steps. The first step is to slow down the film motion by 1/1000 to 24,000/1001 (~23.976) frames/s. The difference in speed is imperceptible to the viewer. For a two-hour film, play time is extended by 7.2 seconds. If the total playback time must be kept exact, a single frame can be dropped every 1000 frames.