Comparison of the CRB reference precisions (left column) on the column density, kinetic temperature, volume density, and thermal pressure, when fitting the ¹³CO (1 − 0) and ¹³CO (2 − 1) lines, with these lines main characteristics (right column): S/Ns, opacities, ratios of the volume density to the effective critical densities, and ratios of the excitation temperature over the kinetic temperature. The blue and red curves show the results for the (1 − 0) and (2 − 1) lines, respectively. The values of the parameters that are fixed when generating the RADEX spectra are listed in the bottom row. The a priori knowledge that are used when computing the CRB precisions are listed in the second row.