Model to Band 6 data of HN¹³CO for S68N in red and data in black. The model uses an excitation temperature that is fixed for HN¹³ CO. Each graph shows one line of HN¹³CO, indicatedby the solid green line at the top middle along with its upper energy level at the top right. The lines with upper energy levels above 1000 K and/or A_ij below 10⁻⁵ are not plotted. The excitation temperature used for this figure is shown at the top left. The dashed green line shows the 3σ level. Cases where a line is seen at the 3σ level or above and is used as part of the fitting are marked with a green X at the top right corner of the box.