<P> A countdown is a sequence of backward counting to indicate the time remaining before an event is scheduled to occur . NASA commonly employs the terms "L - minus" and "T - minus" during the preparation for and anticipation of a rocket launch, and even "E-minus" for events that involve spacecraft that are already in space, where the "T" could stand for "Test" or "Time", and the "E" stands for "Encounter", as with a comet or some other space object . Other events for which countdowns are commonly used include the detonation of an explosive, the start of a race, the start of the New Year, or any anxiously anticipated event . An early use of a countdown once signaled the start of a Cambridge University rowing race . One of the first known associations with rockets was in the 1929 German science fiction movie Frau im Mond (English: Woman in the Moon) written by Thea von Harbou and directed by Fritz Lang in an attempt to increase the drama of the launch sequence of the story's lunar - bound rocket . </P> <Table> <Tr> <Td> "</Td> <Td> People involved in countdowns always say that the last twenty minutes are the worst . By that time everything that needs doing has been done, and therefore everybody has twenty minutes in which to think of what may not have been done, or else what could possibly go wrong . </Td> <Td>" </Td> </Tr> <Tr> <Td_colspan="3">--Willy Ley, 1968 </Td> </Tr> </Table>

Where did the saying t minus come from
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