Comment Re:Misquote in #1 (Score 1) 701
In the Apollo program -- at least, with Saturn V launches -- it's "Ignition sequence start" at T-7 seconds. Those F-5 engines had a complicated ignition sequence which took several seconds just to get the dang things lit. (The pre-burners which turned the propellant turbopumps had to be lit first, and the RP-1 propellant (essentially kerosene) was also used as the hydraulic fluid for gimballing the outboard engines, so had to be pressurized.)
With the Shuttle they started main engines a couple of seconds before T-0 to give them time to come up to power and ensure that they were running properly before igniting the SRBs. Once the solids were lit everything was along for the ride until burn-out (or explosion, as with Challenger).