Slice of the χ² space along the T_eff-log g plane for the example presented in Fig. 4. Contours show 1, 2 and 3σ levels above the minimum determined with procedure described in Sect. 5. The double circle in the center shows the uncertainties given by the main diagonal elements of the covariance matrix constructed by SME at the end of iterations. A larger double ellipse comes from the new uncertainty estimate.