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Both of those, and searching for a solution to a problem which doesn't exist. Nobody can tell reliably whether a cadence variation of 10% affects biomechanical efficiency, so there is no call for a gear system with jumps smaller than that. CVT probably does make it easier to automate gear changing, for people too stupid to work out for themselves when they're slogging/spinning out.

Ah, but it's the thought of smooth gear changes while accelerating hard that gets me dreaming of CVTs.