Top panel: metallicity variations, δ_[Fe/H], as a function of the azimuth, for three different values of the initial metallicity gradient: Δ_[Fe/H] = −0.01 dex (blue line), Δ_[Fe/H] = −0.07 dex (red line), Δ_[Fe/H] = −0.1 dex (green line), and at four different radii in the galaxy disk. Variations are shown at the time of strong bar activity. The values corresponding to R = 7 kpc, R = 9 kpc, and R = 12 kpc have been arbitrarily shifted by 0.5 dex, 1 dex, and 1.5 dex with respect to their real values. Bottom panel: δ_[Fe/H]/Δ_[Fe/H] ratio as a function of time, for an initial metallicity gradient Δ_[Fe/H] = −0.01 dex/kpc. The ratio is shown at three different disk radii: R = 3 kpc (black line), R = 9 kpc (green line), and R = 12 kpc (blue line). This ratio is independent of the gradient, as explained in the text.