Super logical post here, at ESPNcricinfo, about Glenn McGrath being quicker than the 130-something-ish KMPH he was supposed to be.
But just because the speed gun cannot measure nip does not mean humans don’t perceive it. Plenty of batsmen would attest to the fact that they perceived McGrath’s nip all right, even if it didn’t register on the speed gun. So now we know that McGrath was indeed fast, just not in a way that could be measured by a speed gun. This also explains why bouncers are usually slower on the speed gun compared to other types of deliveries covering less ground vertically.