Rotational diagram for CH₃O¹³CH₃ corrected for the optical depth. The data has been corrected for the dust optical depth, as well as the modeled line emission from other species. The filled squares (■) represent transitions detected with SHeFI in the 230, 290, and 345 GHz windows, and the open triangles (△) indicate CHAMP⁺ data. The solid line shows the fit to the combined SHeFI and CHAMP⁺ data, the dotted lines the fit to the main isotopologue by Bisschop et al. (2013) corrected for a ¹²C/¹³C ratio of 20 and 30, and the dashed lines a ¹²C/¹³C ratio of 10 and 40.