Upper panel: comparison between the EW_862.1 measured by DIB-Spec and the mean EW_862.1 in each voxel taken from the DIB catalogue in DR3 for 8963 voxels. The colour represents the number density (estimated by a Gaussian KDE) of the data points in a linear scale. The grey colour bars show the EW uncertainty in DIB-Spec and the standard deviation of EW in DR3. The dashed red line traces the one-to-one correspondence. A zoom-in panel shows the distribution of the EW difference (ΔEW = EW_FPR − EW_DR3). The mean (Δ) and standard deviation (σ) of the EW difference are indicated. Lower panel: the variation of the mean EW difference in each EW bin with a step of 0.01 Å with EW_862.1 in FPR. The orange shades the range of 1σ.