Rare forms of oxygen, called isotopes, in carbon dioxide help scientists understand important atmopsheric processes, for example where CO₂ comes from. In this paper, we examined how to improve the accuracy of a laser-based method for measuring oxygen isotopes in CO₂, focusing on the rare mass-17 isotope. By testing instruments in two labs, we identified ways to make the results more reliable. Our findings provide practical guidance and support wider use of this method in environmental studies.