Internal error at 70% of the error distribution as a function of the SNR for cool dwarf metal-rich stars (T_eff ≤ 5500 K, log g ≥ 4.0 dex, [M/H] ≥ 0.0 dex, green diamonds), cool giants with intermediate metallicity (T_eff ≤ 5500 K, log g ≤ 3.0 dex, 0.0 > [M/H] ≥ − 1.5 dex red stars), hot subgiants metal poor (T_eff > 5500 K, 4.0 > log g ≥ 3.5 dex, [M/H] < − 0.75 dex, black crosses), and the whole sample of interpolated spectra (blue triangles).