Plot of the mean F_10.7 background flux for spotless days (red dots) as a function of the duration of the sequence of contiguous spotless days. The errors bars correspond to one standard deviation. The upper curve (blue dots) and lower curve (green dots) are the lowest and largest F_10.7 values for each spotless duration. The red dashed line marks the overall mean spotless flux (70.5 sfu), while the lower black dashed line is the mean minimum flux (67 sfu). The lower panel gives the number of intervals for each spotless duration (red bar) and the number of days included in each duration (green).