Schema summarising the evolution of the B_z distribution with a log-log plot. It shows the difference in the distribution between a newly emerging AR (green), one at around the time of peak flux (yellow), and one during the decay phase (blue). After this time, the field distribution of the AR evolves towards that of the quiet Sun (red). Since both magnetic polarities have very similar distributions at a given time (e.g., Figs. 4 and 8), they are not separated in this schema.