In my opinion, this is still one of the most commercial magic tricks available. I started doing this as a high school kid in the mid 1970’s, and it is still in my act. In fact, I remember in the mid-1990’s attending a taping of a David Copperfield TV special in Tampa, Florida. During a break in the taping of the major illusion sequences, Copperfield himself came out and performed this effect! In performance, you show a card that has one spot on the front, four on the back, but now three on the front and six on the back. You perform it again, then offer to show how it’s done. You explain that the card really has two spots on one side, and five on the other. By covering either a spot or a blank space, you can show one or three spots on the front, and four or six spots on the back. However, when your hand is removed, the audience sees you really have three spots on one side, and six on the other! Once more, the card is turned over and you end with EIGHT spots! This effect always gets laughs, gasps of amazement and a big hand! Packs flat, always ready to go, no flaps.
Spots keep multiplying on this card, from 1, 2, 4, 6 and finally 8!