Spectral subtype sequence for the wavelength region around K I VIS_red. There is an offset added to the normalised spectra for convenience, which is larger for the M7.0 spectrum. For comparison we show PHOENIX models in black for two of the stars; more details are given in the main text. The shown spectra correspond to the following stars from bottom to top (Karmn number and corresponding line colour in parenthesis): M0.0 V: HD 23453 (J03463+262, purple); M1.0 V: GJ 2 (J00051+457, blue); M2.0 V: GJ 47 (J01013+613, dark blue); M3.0 V: G 244-047 (J02015+637, cyan); M4.0 V: LP 768-113 (J01339–176, green); M4.5 V: YZ Cet (J01125–169, lime green); M5.5 V: GJ 1002 (J00067–075, orange); M6.0 V: CN Leo (J10564+070, brown); M7.0 V: Teegarden’s Star (J02530+168, red); M8.0 V: vB 10 (J19169+051S, dark red).