Comparison of the linewidth W_20,data at the 20% height estimated from the observed THINGS spectral line to W_20,fit, the same value for the profile fitted in the present paper to that line. The fractional linewidth difference was calculated from the expression 2(W_20,fit − W_20,data) / (W_20,fit + W_20,data). Values for W_20,fit are given in Col. 10 of Table 1, and the fractional difference itself is given in Col. 11.