Space-time slices showing the temporal evolution of the magnetic flux along annuli with radii of 5.75 Mm (bottom) and 7.25 Mm (top), respectively, which are centered on spot A. HMI magnetograms with a cadence of 45 s covered a period of 12 h starting at 04:00 UT on 2010 November 18. The annulus with a width of 0.5 Mm was cut open in the east and then transformed to a straight line such that the southern part of the spot was mapped to the lower half of the space-time map. The heliographic direction is indicated on the axis to the right.