Relationship between I_CO(3-2) and I_CO(2-1) for the SW bar and N66. The integrated emission in both transitions has S/N > 3. The green dots (indicated as low uncertainty) correspond to integrated emission with relative uncertainties <20% in both transitions. The white dots indicate integrated emissions with higher relative uncertainties. The solid and dashed red lines show the best fits of the low uncertainty data assuming a linear and a power-law model, respectively.