Analysis of casino shelf shuffling machines (projecteuclid.org)

TL;DR: Lots of math is used to show that a novel mechanical card shuffler using psuedorandom numbers needs to be run twice in a row to be effective at preventing players from guessing the resulting cards.

A lot of what we call Card Shufflers are actually Card Rifflers - interleaving 2 halves of a deck together.

Juan Tamariz has made a career in card magic based on most people not knowing the difference.