Comparison of observed and predicted OV line intensities for active regions No. 1 (top panel), 2 (middle) and 3 (bottom), using 4′′  ×    4′′ pixels. Intensities are in units of erg cm^-2 s^-1 sr^-1. The dashed line is I_low = I_bou − 3σ_bou (Eq. (4)), and dash-dotted line is I_up = I_bou + 3σ_bou, where I_bou is given by Eq. (5). Simulated intensities are sorted in the ascending order. Crosses are corresponding observed intensities sorted in the same order as I_low. The continuous lines are predicted intensities for optimal fitted δ and λ, sorted in the same order as I_low.