Measurements of LFC line positions. Left: measurements of 17,807 individual LFC peak positions, v_n (black circles). Weighted means for bins of 5 Å in width are shown as gray circles. A linear fit to all measurements is shown as a red line; the small slope determined is not visible on this scale. The spectrum of the LFC is overplotted (orange) in linear arbitrary units. The width of the LFC peak position distribution is wider in the areas of lower signal. Right: histogram of residuals between observed and true LFC positions, v_n , after subtracting the FTS zero point, v₀ and normalized by the uncertainty of the measured line position, σ_n . The red curve indicates a Gaussian distribution with a 2σ interval indicated by the red vertical bars. The distribution is only 5% broader than expected from uncertainties, σ_n.