Relation between ratios R2 and R8 (above, left), R3–R9 (above, right), R5–R11 (below, left) and R4–R9 (below, right) for the Maxwellian distribution (thick black lines) computed for the solar atmosphere with a constant pressure characterized by N_e × T = 10¹³–10¹⁶ cm^-3 K with the DEM 3 (full lines), DEM 2 (dot-dashed lines), and DEM 1 (dashed lines). The points correspond to DEMs with N_e × T = 10¹³, 10¹⁴, 10¹⁵, and 10¹⁶ cm^-3 K. The crosses with error bars show observed line ratios.