[Keyframe]

Technically, it's eight eights that are one minute of screen time - WHEN you keep dialogue to ~three lines per spoken part and you write only what you see.

In general though, if format isn't what it is you wouldn't be able to gauge how long a script lasts and you wouldn't be able to break it down for production easily.

[skepticaldrunk]

True, but if we're getting really technical, the script supervisor gets to decide what an eighth is, so a decent scripty will keep it shockingly consistent. Another quirk, for sure, but when you see the breakdown and it lists 120 pages worth of scenes on a 114 page script, it actually makes sense.