Measurement of the line core brightening (LCB) with respect to the line wing brightening (LWB) in the Hβ line for the QSEB shown in Fig. 4. The distance d between LWB and LCB is the separation between the centers of gravity of the areas with RPs 9–15 (LWB, green) and RPs 16–23 (LCB, red) at the times of their first appearances. The time separation between these first appearances (77.4 s) is used to determine the average propagation speed, here 2.6 km s⁻¹. The orientation is measured against the horizontal direction as shown, the direction toward the nearest limb is 36° (black arrow). The histograms of the measurements of all QSEBs with line core brightening are shown in Fig. 7.