Histograms of Δ (≡simulated minus original value) for the main scalar properties derived from the spectral synthesis: ⟨log t⟩_L, ⟨log t⟩_M, log ⟨Z⟩_L, log ⟨Z⟩_M, A_V and the initial stellar mass formed (log M′). Each row corresponds to one set of simulations, alternating S and O runs (as labeled in the y-axis). Mean Δs and their σs are labeled in each panel. Except for the A_V column, each histogram is based on 16 380 values obtained from the 1638 zones in CALIFA 277 and ten Monte Carlo realizations of the perturbation. For clarity, the A_V histograms were drawn excluding the many ΔA_V = 0 cases, which occur due to the A_V ≥ 0 physical limit imposed on the spectral fits. Noise-free simulations (OE0 and SE0), which trace intrinsic degeneracies in spectral fits of composite stellar populations, are shown in the top two rows. Random-noise simulations (SR1 and OR1, central rows) map the uncertainties caused by statistical fluctuations of the observed F_λ fluxes. C002-simulations, where the spectral-shape is changed to emulate calibration uncertainties, are shown in the bottom panels.