This is an incredible feat of mind reading that's so easy and practical to do. Sells on sight when demonstrated in our 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.