Evolution of photometric area and magnetic flux for the four regions A (solid), B (long-dashed), C (dashed), and D (dashed-dotted) over an eight-hour period on the 6 September 2017. Regions A – C indicate penumbral decay, whereas D is a site of umbral strengthening. The time profiles were significantly smoothed to avoid clutter. The original data points are shown as plus signs for region A to give an impression of the scatter.