What does the fortune teller mean by measuring his hand with a ruler?

The fortune teller measured his hand with a meter ruler, but how did he know his last name?

There are 24 squares painted on the red plastic sheet in front of the fortune teller, and each square has 20 surnames, totaling 480 surnames; And he prepared a total of 10 cards, each card has 48 surnames, a total of 480 surnames, and each card has a number. This kind of fortune-telling procedure is very simple, with only three keys: cover the grid with the surname; Measure the size of the hand; Identify surnames on red plastic paper. The fortune teller first asked the calculated person to find the card with his surname from the 10 card, and then covered the card with his surname on the grid on the plastic sheet; The fortune teller picked up the card covered on it and said the surname of the person being counted; Then the fortune teller measured the palm width and the length of each finger of the calculated person with a soft ruler according to the convention of "male left and female right", and according to the size of the hand, picked out the small pieces of paper prepared in advance and gave them to the calculated person, and this time "fate" was completed. The secret is that each card has a number mark, and the fortune teller can know the calculated surname as long as he remembers which surname each card overlaps in different positions. The fortune teller used the simplest intersection method in mathematics. The reporter found that in just ten minutes, five or six citizens saved money; Some citizens also left directly after reading it. It's a trivial matter that the cheated person is short of two yuan, but it can't help this bad style of cheating. I hope everyone will keep their eyes open and not be confused by these quack tricks.