Correction of results by taking into account the difference between the predicted and measured f₀F₂: (a) ∆f_calc deviation from ∆f_meas versus the difference between F₂ layer critical frequency f₀F₂ estimated by the IRI-2012 model and that measured by DPS-4 Digisonde^®; dashed line is the regression line running through the origin of coordinates; thin lines are 99% confidence limit lines; (b) the same as in Figure 3, but with correction taking into account the Δf_calc − Δf_meas difference dependence on the IRI-2012 model’s inaccuracy in f₀F₂ estimates.