Using Madore's psi function, the ordinal \(\psi(\Omega_{\omega})\) is a large countable ordinal that is the proof theoretic ordinal of \(\Pi_1^1\)-\( ext{CA}_0\), a subsystem of second-order arithmetic. The subcubic graphs, which are used in definition of SCG function, can be ordered so that we can make bijection between them and ordinals below \(\psi(\Omega_{\omega})\), as well as Buchholz hydras with \(\omega\) labels removed. It is the first ordinal \(\alpha\) for which \(g_{\alpha}(n)\) in the slow-growing hierarchy catches up with \(f_{\alpha}(n)\) the fast-growing hierarchy, under the most common usage.