Two-dimensional histogram of vs. 2D representing the complete comparison between the data cubes obtained with the IRAM 30 m and APEX telescopes observationsof the transition ¹²CO(2–1) in the extended G region. The two cubes were resampled to the same spatial and spectral resolution. Every spectral channel in every single pixel is compared and shown in the histogram. The dashed black line represents the 1:1 relation expected between the two spectral cubes if the data was identical. The solid black line represents the empirical relation that is measured by determining the best linear fit corresponding to the data dispersion, using a threshold of 1.5 K to best describe the high signal-to-noise bins.