How does it work?
I see a sequence of 2-4-6-8
Then a 3; the third number after that is a 6; the third after that is a 12.
I don’t see an obvious pattern otherwise.
The teacher would use a pointer to point at x2, or x3 etc. and then randomly point at a number on the outside of the circle. At the beginning of multiplication, the teacher would drill the class using the circle just using x3 for example. But once the class had mastered facts up to x9, the circle you see on the blackboard would be used. This way, the teacher, or a student could really mix the problems up. Today, by using a computer and a smart board, you could duplicate the same thing for just a few thousand dollars.