A fellow subtitler asked me: Are you really in favour of 13-15 cps? And I think I said I'm against cps as a hard and fast rule. May sound radical, but it's actually old-style #subtitling. All about priorities: Emphasis on words or image? Where is the important stuff happening?

Metaphors are dangerous, but It's like cooking dough. No exact ingredients, as it depends on room temperature, humidity etc. Experienced subtitlers know when text is readable within the time it appears onscreen. Short+complicated needs longer than long+straight-forward.

But there's no easy way to measure complexity in all languages (or difficult to implement technically) so the easy way was chosen: cps