Example of rotation diagram fitting in the Ser-SMM3 outflow. The aperture shown is marked by a red cross in Figures 1 and 2. The observed data points and the data after correction for extinction and a non-LTE ortho-to-para ratio are indicated by the red and blue points respectively. The best fit to the warm and hot components are show as dotted and dashed lines respectively, while the solid line indicates the best overall fit.