Although this close-up divination effect is simple, it is quite puzzling to lay people, particularly because it is immediately repeatable, and will pass most examinations by the audience if they choose to go there. The effect is quite clear and easy-to-understand:
The amazing Mental-Magician shows five specially designed card holders, each holding what appears to be a playing card. (see photo, as that will be better than me trying to describe the design of the holders). When the cards are removed from the holders, it becomes clear these are not regular playing cards, but special ESP testing cards. Each card has a single digit number on each side -- the numbers on opposite sides of each card are different from one another. So there are 10 different numbered sides, and the spectator is told that she can arrange the cards with any numbers facing upward that she chooses.
As she decides on each number to leave faceup, the card is slid into the holder, and the design of the holder has a "number cover", so the numbers are completely hidden. All five cards are put into holders, hiding the five chosen numbers. All this occurs when the magi-mentalist is turned around and cannot see. When the Mental magician turns back to the spectators, he picks up the five folders, and he immediately knows the sum total of the five numbers.
Can be repeated, and should be, as the mystery is heightened with a few repeats. If you are familiar with the Swami gimmick, or Boon writer, etc, you can incorporate it into one phase of this effect, to apparently predict in advance the sum of the spectator's numbers. (That is not explained in the instructions, but if you know the Swami gimmick, you will know how to do that)
Also not explained in the instructions, but if you bought two of these, you could take some cards and holders from the second set, and extend the effect to use 7 or 8 number cards instead of just 5 cards... (But you have to buy two sets for that. Hint, hint)
A good-looking set of props, easy to do, and easy to carry in your pocket, so you can always be ready for a quick demo of mental divination.