Literature ¹²C/¹³C ratios towards sources at different evolutionary stages using different isotopologues. Simple O- and N-bearing species (<6 atoms) share a light blue and light yellow colour, respectively, but have different markers. Black rectangles around the orange triangle (N) and coloured circles (O) indicate complex organics (>6 atoms). Arrows indicate lower limits. References to the values can be found in Table A.9.