Correlation between the yearly number of active regions and the F10.7 flux. Left: scatterplot between the active regions and the F10.7 flux (green asterisks), together with the corresponding best-fit line (black). Right: difference between the yearly number of active regions and the correlated F10.7 flux. Best-fit line (black) and lines with slopes that are two standard deviations above or below the best-fit line slope (two blue dashed lines) are also included.