Statistical equilibrium calculations of optical depths and line ratios. The left and right panels show that the calculations are performed under the specific column densities of 10¹⁵ and 10¹⁶ cm⁻² km⁻¹ s, respectively. The coloured background shows the regions with negative optical depths of the 104.3 GHz methanol transition where masers can be generated. The black and white contours represent the peak intensity ratios of T_r,104.3/T_r,84 and T_r,95/T_r,84, respectively. The red star is the intersection of the observed two pairs of ratios in G10.34−0.14, and the red dashed lines represent the 1σ uncertainties of the observed ratios.