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Faust76 · 46-50, M
Active rockets usually involve very precise sequence of events which need to happen after the launch. Positive count needs to start at the launch, so it makes sense to count reverse up to that. Increasingly complicated sequence is also needed before launch, so that really needs a count to. Also it's just a nice way to know exactly how long you have left.
KA9ha · 31-35, M
@Faust76 you are partially correct upto a point.Actually,before the fire ,there are six points of pre-sequence like actuator on,oxygen on,igniter on,director on ,sensors on,thermals etc which have to be switched in last 15secs after time gaps .. these are coordinated before reaching all clear zero ....fire