Difference (literature – this work) in T_eff (left panel), log g (middle panel), and [Fe/H] (right panel) on the y-axis vs. the respective parameter estimates using our method (x-axis) for the six nearby M giant stars in the IGRINS spectral library. Differently colored symbols represent the compiled literature estimates: red circles show Baines et al. (2021), blue squares show Lebzelter et al. (2019), green diamonds show Jönsson et al. (2014), inverted yellow triangles show Sharma et al. (2016), and brown diamonds show Guerço et al. (2019). The black circles denote the T_eff estimated using the T_eff vs. (V-K)₀ relation in Eq. (2) (from Bessell et al. 1998). K_2MASS has been corrected to the photometric system in Bessell & Brett (1988; https://irsa.ipac.caltech.edu/data/2MASS/docs/releases/allsky/doc/sec6_4b.html)