Notes. Ca II H & K: Bjørgen et al. (2018), He I D₃: de la Cruz Rodríguez et al. (2019), Hα & Hβ: Capparelli et al. (2017), NaD₁ & NaD₂: Bommier (2016), Mg I & Ca I: Sampoorna & Nagendra (2017), Fe I 6301 Å: Grec et al. (2010), Fe I 6173 Å: Fleck et al. (2011), C I: Joshi et al. (2011). It is important to note that the formation heights provided here are intended to provide a general guide for the readers. Activity and structure variations impact the line formation heights, but will not vary so much that a chromospheric line like Hα to form at a lower height than a photospheric line like Fe I 6173 Å. These variations typically preserve the height ordering presented.