Simple cards

It looks the same as ordinary poker, but there are hidden trick on the back of the poker.
Ordinary people don't notice this because the points are small.
No matter which one of your audience comes up with, you can know the number of points at a glance. 
No matter how the audience looks at the card, he will not think that the hidden trick is on the back.
Very simple but unexpected.
As shown, the back of the playing card has a row of diamonds, each diamond corresponding to a number. The seventh diamond is larger than the other diamonds, indicating that the number is 7.
Spades, diamonds, clubs and hearts is also the corresponding diamond.