Example of ¹³CO spectrum (top, in blue) extracted from the GRS, along with the combined fit to all lines (red) for the Hi-GAL source detected at l = 29.9388°, b = 0.0167°. The green dashed lines indicate the individual Gaussian components that make up the overall spectrum. The ¹³CO spectrum exhibits several lines with very different velocities; thanks to the observed NH₃ spectrum (bottom) the velocity of the source can be determined (98.41 km s^-1).