A histogram showing the distribution of “wiggle fraction” J among the THINGS galaxies, as specified by Eq. (8). This quantity indicates the approximate extent of local fluctuations of H i density away from the fitted model. Values shown here as less than zero are technically imaginary (see the respective values in Col. 8 of Table 1), since they are square roots of differences in quadrature which turned out to be negative. Such values simply indicate that fluctuations away from the model fit are, for that galaxy, dominated by measurement noise.