Mixed L−σ relation for the combined Chavez14/SDSS (black squares) and BT11 sample (red triangles) of 132 HII galaxies. The lines show the LSQ and ML fits as in the previous figures and the relevant parameters are given in Table D.1. The green dots correspond to the 16 giant HII regions of the Hippelein/Arenas sample used to calibrate the zero point of the relation and thus establish the value of H₀. The inset shows the χ² curve (actually ) and the value of H₀ determined from a cubic fit to the curve.