Density scatter plots (2D histograms) of restored longitudinal magnetic field vs. model longitudinal magnetic field taken at the effective formation heights for the wavelengths 8.6, 4.5, 3.2, and 1.3 mm. The wavelength is indicated at the top of each panel. Darker shading indicates a higher density of pixels in the bin. Solid lines denote the expectation value, . Dashed lines depict the linear regressions with the slopes and the Pearson correlation coefficients given in the upper left corner of each frame.