I saw Marc Oberon deliver a lecture at the Magic Circle recently and he explained the principle behind his Master Deck. I went home and made up the deck as he described (as best I could remember) and started practising locating random cards. Loved ones soon get annoyed with being asked to call out random cards all the time, so I wrote a little program to help me develop my location speed. I suppose it could be used for honing all sorts of other effects too. Whatever. Have a play with it. I hope you find it useful.