Inversion results for Model A, using the modes with n = 15−25 and ℓ = 0−2. The x axis gives the mean density of the reference models divided by that of Model A, while the y axis is the mean densities obtained from the various inversion procedures, normalised by that of Model A. For each procedure, there are three lines corresponding to the result and the 1σ error bar around it. The horizontal triple-dot-dashed line shows the correct mean density. A ν^−b + 1Q_nℓ normalisation has been used when surface corrections are included in SOLA inversions.