Note from Martin:

Any card is merely thought of by a spectator, they are handed your set of Computer Cards, each one of these has various cards randomly printed on it. They look for the ones containing their thought of card and place them aside. Amazingly, you now read their mind and name the thought of card.This is a modern card magic version of a classic age cards magic trick, it has novelty value and is ideal for both beginners and experienced magicians. This is an incredible feat of mind reading that's so easy and practical to do. Sells on sight when demonstrated in our London magic shop.

The effect is of a freely thought of card being revealed by the magician after merely handing the specially printed Computer Cards to a spectator who on looking at them removes the ones with the thought of card on.

 

This may read as though it's an obvious principle, but when you see the effect performed, you'll be amazed at how baffling it is to the audience. When you know the method, you'll be impressed at how clever the working is.