Topic on Talk:Final Fantasy XIII
Where for "correct rate" I think ±25% could even be accepted: but the problem in your shot (which is no longer available btw) is that frametime is sampled only once for second. That hides completely every issue with single frames that may happen.
The game may actually be requesting a frame every 16.6ms... but if one drops.. (and we can't be sure due to aforementioned reasons) then you would have to wait 33.3 ms.. and that's a big difference.
Nothing like that 2ms differences you seem to be worried of (and that really, I can't understand how could be perceived by humans)