I have seen the link, it is very clever but complicated. Basically the cards are stacked back to back in a special order. The cards are rough-backed so that this does not show when spreading them. It then works on a system of odds and evens, with the magic total being 13. Clubs and diamonds are odd, hearts and spades even. Thus the 10 of diamonds will be back to back with the 3 of clubs. If someone chooses the 10 of diamonds, then the pack is opened odd numbers up, the key card being the 3 of clubs. The cards are then spread and when the performer finds the 3 of clubs he carefully peels off the card below it, which appears to be the only one upside down, but in reality all the cards are upside down, depending on which way you open the box.