Fractional difference between the flux S_data, derived from summing the flux densities in each data channel, and the value S_fit, the equivalent sum of flux densities from the fitted line-profile model. This fraction was calculated from the expression 2(S_data − S_fit) / (S_data + S_fit). The x coordinate is the fitted flux S given in Col. 4 of Table 1, whereas the fraction itself is given in Col. 9. S_fit is identical to S except in the cases of DDO 53, NGC 2976, NGC 3077 and NGC 6946. For these galaxies, some channels around velocity zero were omitted from the calculation of both S_data and S_fit. Uncertainties were calculated from the two independent contributions using the standard propagation formula.