Morphological stability of sample clusters on three different projections within tidal radii vs. logarithm of the age of the sample clusters. The meaning of the values in the labels, symbols, and curves of the picture are the same as those of Fig. 5. The age parameters of the sample clusters are from van Groeningen et al. (2023). The solid red lines are linear fit lines. It should be noted that the number of samples in each panel is not equal to that of all samples. Because we removed those samples with the central core area ($S_{cor{e}_{xy}}$, or $S_{cor{e}_{xz}}$, or $S_{cor{e}_{yz}}$) being zero.