When I first read about this, I thought it was a bunch of "horse pucky"  but supposedly it works.  I just hope your math skills are sharp! 

Have you ever gone to StumbleUpon.com?  Its a great site where random stuff comes up and you "stumble upon" it.  The FIRST thing I saw was this - a formula to determine if the credit card someone is passing off is fake.  This is great for you have your own business and you're trying to protect yourself from being ripped off.

According to an article at Creditcards.com, there is a "Da Vinci Code" of sorts to tell whether someone tried to hand you a fake piece of "plastic".  It seems confusing at first, but it's easy if you think about it

 

Ok, this is a fake credit card number.  (Can you tell?)

Now if you copy the instructions from mint.com you can determine whether it's fake.  (Wow, I just made this credit card number up.  Watch - it turns out to be a real card!  I'll die!!) .  Wheew. I did what they said, and it is fake!

How awesome- A formula to tell if you're getting ripped off or not - don't leave home without it!