Abundance corrections for two fictitious lines of neutral iron (χ = 0 and 6 eV) and one of ionized iron (χ = 6 eV) at 400 nm, plotted versus the mixing-length parameter α_MLT used with the 1D LHD model atmospheres at [M/H] = 0.0 (top row) and [M/H] = −3.0 (bottom row). Three types of abundance corrections are shown: Δ_{3D−⟨ 3D ⟩} (left column), Δ_{⟨ 3D ⟩ −1D} (middle column), and Δ_3D−1D (right column). Note that Δ_{3D−⟨ 3D ⟩} abundance correction is not influenced by the choice of α_MLT (there is no comparison 1D model atmosphere involved); we nevertheless show all three abundance corrections to provide an indication of the absolute size of abundance corrections involved and the range of their variations with α_MLT.