Example of the GOF and FT measurement methods applied to the He iλ4713 line of VFTS 280 (top row, high S/N) and VFTS 163 (bottom row, poor S/N), to illustrate two different data qualities. Left-hand column: line profile (black) and its GOF solution (red). Right-hand column: Fourier transform of the observed spectrum (black) and of the best fit GOF profile (red). The dashed lines indicate the position of the FT first minimum.