This diagram shows two combinations of waves and the results. It does this using the circles containing arrows from Figure 6. Both situations are depicted as simple mathematical sums, i.e. wave 1 + wave 2 = result. Figure (a) shows one circle containing an arrow that points up, and one circle containing an arrow that points down. circle 1 + circle 2 = one circle containing both arrows equal in size and pointing in opposite directions = no circle remaining, as the waves have cancelled out. Figure (b) shows two circles containing arrows that point up. circle 1 + circle 2 = one double-size circle containing both arrows stacked together = one double-size circle with one double-size arrow.