Great simple method for an impressive trick - but dramatically I'd reverse the sequence. Solve the
magic square (miracle) , THEN reveal the card at the nth position. The prob for me with magic
squares is that you never quite know when to finish. The audience are often ahead of you and have
done the math - in all directions. Plus, they kind of expect it to work. The reveal of the selected
card at the right position is clean, instant and finite.