Sunspot group dynamics during the formation stage. Left panel: HMI intensitygrams of the active region NOAA 11260 with two sunspots (A and B). The XY coordinates are reverced. The frames obtained in period of 2011 Jul. 28–2011 Jul. 30. The active region field-of-view is [200″ × 100″]. The active region center coordinates are [−278″ × 209″] obtained at 20:00 UT on 2011 Jul. 28. The arrow in the first frame shows the small magnetic element, which is actively developing in time. Right panel: time series of the magnetic field strength (absolute maximum values) obtained from the magnetograms of the spot A (solid line) and the spot B (dashed line). Arrows show the quasi-regular delay between the variations. The time series start at 00:00 UT on 2011 Jul. 28.