Thank you. It's been an important thing to know. It's one more usage of modulo I have never thought of as a programmer. And it would become important if I didn't use the library MD_MAXPanel.h which makes the display a 32 x 8 matrix. In fact, without this library each of four 8 x 8 modules has its own index from 0 to 3 and I would have to use this mathematical operation to make a transition between any two of them.