Back in the Grey Matters' 6th Blogiversary post, I mentioned that James Grime had something up his sleeve for this year's Pi Day, as well. He slightly missed the deadline, but has delivered nonetheless.

Let's start with James Grime's own rather unusual description of this year's Pi Day trick. He starts the video with an apology for the delay, and then goes on to explain the trick with puppets (yes, puppets):



To answer your first two questions, yes this is a real trick, and yes, the app is real. The app is called Pi Day Magic (iTunes Link), and is available for free on the iPhone, iPod Touch, and the iPad (running in 2× mode)! At this writing, the app is expected to be released for other smartphones soon.

Knowledgeable magicians and longtime Grey Matters readers will recognize this trick as the Fitch Cheney Card Trick. In that 2008 write-up, I tried to write it step by step, so you can understand the trick completely in as clear a manner as possible. The secret is also explained more briefly in the app itself.

Normally, performing this trick requires two people. Using the app instead, the smartphone or tablet you're using takes the role of the secret helper. I do believe using a secret helper is more effective here, because it more effectively takes the mathematical air off of the trick.

That said, the app is a great way to practice the trick. As the performer, you can practice reading the order of the cards (which you still need a second person to select) to get the knowledge of the 5th card. As the secret helper, you can also use it to help make sure that the cards are being arranged in the proper manner.

Practicing as the secret helper with the app, however, can be a little tricky. It's often possible to arrange the cards in more than one way, and the app will only arrange the cards in one of the possible ways. This doesn't necessarily mean that you arranged the cards wrong, just that the program chose a different target card.

If you've made the effort to learn this trick as described in the app or my post, here's a puzzle for you (no fair using the app to figure this out): Take out the same cards used in the video above (KH, 6C, 4C, 4D, and 9H). Arrange the cards so that another card, instead of the King of Hearts, is face down. Which card is face down, and how are the other cards arranged to communicate it?

Post your answer in the comments, and I'll acknowledge the first right answer I receive. If no one gets it, I'll post the answer at the end of Sunday's blog post (March 27th).