You'd probably want Characters per minute. Anyway, I'm one-finger-tap-typing this reply on a tablet while reclining on a couch, so I don't know how APM would be relevant to always be shown, as it doesn't reflect proper typing speed. As mentioned, editing and deciding what to post will also kill APM numbers. While promoting thoughtless and poorly edited / typed replies by those who will want to top the APM charts. Which is just silly.