Measured NGC 253 isotope ratios in the ACA data (Table 4) compared to their equivalent values in the Milky Way (Wilson 1999). The horizontal axis indicates the molecular species, or in the case of CO the isotopomer, used to measure a given isotope ratio. Colored rectangles are used to indicate Milky Way isotope ratio value ranges. As no uncertainties nor range of values was provided for the Si isotope ratios, a range of 10% of the estimated values was assumed. As the Milky Way ¹⁶O/¹⁷O value would be ≳875, we have opted to not show this Milky Way isotope ratio value.