The number in the center is the beat number. Beats per measure goes up to 12. Tempo goes up to 360. Don't make the tempo too low. If you do, even if you set the tempo higher again, it could be a while before it gets that high again. And DEFINITELY don't set it to zero, because that divides the time between each beat by zero. If you do by accident, the green flag won't help you. You have to reload the tab.
@diggindagon helped a little. (I can't remember what he helped with though)
