Full width at half maximum (w) of the activity belts as a function of the mean unsigned latitude of the sunspots each year. Different colors represent different cycles as in Fig. 3. The thin black curve is an approximate fit to the declining phase: w = 1.1λ_c. Error bars on the top left indicate standard deviations of λ_c and w, respectively, from the Gaussian fit procedure carried out for each year; maximum values are shown in red while the mean values over all years are given in black.