A Function：There is a special contact lenses can see which card it is,even though the card is back to you. B Size：As the normal plastic cards you can see in the market. C Advantage: 1.The marked letter is big enough to see 2.Can be use in any card game and nobody will feel any different 3.Only the user wear the special contact lenses ,then can see not only his cards ,but other people cards which was marked. How to use It is very easy to use ,the user just wear the special contact lenses ,then put the cards where you want ,the you can see and marked as you know.