Histogram of the normalised relative difference between the main beam temperature of the ¹²CO (1–0) line measured in the FQS and in the FUGIN survey. The data are resampled to a common spatial resolution (55″), pixel size (17173), and velocity channel (1 km s⁻¹). All voxels (l, b, v) with emission above 5σ for both sets of data are considered. The continuum line shows the best-fit Gaussian distribution with peak at 0.01 and standard deviation of 0.23.