MARVELOUS ACAAN by Joseph B
In this effect the spectator is able to find the card that he himself has chosen.
The conditions appear impossible because the spectator cuts the deck where he wants and gets four predictions. Then he shuffles the deck and loses the card he has chosen in it. The sum of the value of the four predictions will indicate where the chosen card is, the exact position.
MARVELOUS ACAAN is a semi automatic effect that is very easy to do.