This is a classic mental effect where three spectators each write down a number and a fourth spectator makes the addition. this sum matches your prediction. So far so good.
We have created a NOTE BOOK in finest calf leather. Inside is a pad of Post It papers (3 x 5 inches). At the opening side of the note book there is a holder for the pen. When the pen is in place it also locks the note book.
Now to the handling: Ask three spectators to write any number between 1 and 1000. When the last spectator is ready, he puts the pen in place and throws the book to any person in the audience. He or she opens the note book and makes the addition. IT MATCHES YOUR PREDICTION!!
What really happens is that the note book has built in magnets that automatically switch the side of the Post It pad when the last person opens the book. It is safe and easy to do. thanks to the locking pen there is no risk the note book will open when they throw it.And remember you never touch the note book after the third person has written his number!
BONUS!!! There are additional routines from Gay Ljungberg, including his Burnt Borrowed Bank Note Routine in which the Add-a-Number Note Book is used to verify the serial number of the restored bank note.
Highest quality calf leather note book made by a Swedish craftsman.