Results of measurements performed to test the reliability of inner-width estimates from both Plummer and Gaussian fits to the profiles of 180 Plummer-shaped synthetic filaments with variable D_flat diameters along the crests. The synthetic filaments had a fixed input central column density contrast C⁰ = 1, a fixed indexp = 2, and a power-law distribution of individual input D_flat diameters between 0.022 pc and 0.19 pc with an exponent of − 2 (in ΔN∕ΔlogW, similar to that in Fig. B.4B) along each crest. The distribution of input inner diameters is shownby a dashed black histogram in all three plots. Left panel: histograms of measured D_flat diameters from Plummer fitting. Two sets of results are provided for D_flat as explained in the caption of Fig. B.5. Middle panel: histogram of median FWHM values derived from Gaussian fits after averaging along each filament crest. Right panel: histograms of individual FWHM values measured along the filament crests. In this plot, the dashed black histogram of input D_flat values has been rescaled so as to have the same peak as the red histogram of measured D_flat values.