Function C_H(i) (Eq. (11) for hydrogen levels only), corresponding to: the new ALI scheme for spectral lines based on the local operator (LOC), the old ALI scheme for spectral lines based on the core saturation operator (CSA), no acceleration in spectral lines (no-ALI). LSP denotes the acceleration with local operator in case when the spectral lines are treated in the statistical balance system with single precision instead of double. The small wiggles of LOC curve after the convergence limit has been reached is due to the update of the Eddington factors (see e.g. Hubeny & Mihalas 2014, p. 418) each 10th iteration. The same holds true for the smaller wiggles along CSA and no-ALI curves. The dashed lines denote the convergence limits used for the calculations with single and double precision.