Top panels: Magnetic field structure functions as a function of distance l of SDC18 (black) at filament scale (black) in panel (a), and of SDC18-N (red) and SDC18-S (blue) at isolated clump scale in panel (b), and of SDC18-N-1 (orange), SDC18-N-3 (yellow) and SDC18-S-1 (cyan) at clump-embedded core scale in panel (c). Solid lines are the best fits of Equation 10. Dashed lines show the ordered component ($\frac{1}{N}\frac{\langle B_t^2\rangle }{\langle B_0^2\rangle }+a{l}^2$) of the best fits. Bottom panels: correlated component ($\frac{1}{N}\frac{\langle B_t^2\rangle }{\langle B_0^2\rangle }{e}^{-l^2/2({\delta }^2+2W^2)}$) of the best fits. Data are binned to half of the synthesized beam in the right panels (isolated clump scale and clump-embedded core scale) and to one beam in the left panels (filament and filament-embedded clump scale), and plotted at the average distance within a bin.