An example of the iterative detailed modelling of the λ6750.2 Fe I line in 51 Peg. The observed line profile is shown in black with solid markers, and the line profiles synthesised with varying input atomic parameters are shown in coloured lines (corresponding to different log(g f) values). The panels show three of the synthesised wavelength values: λ_input −0.05 Å (left panel), λ_input (middle panel), and λ_input + 0.05 Å (right panel). Each panel shows the full −0.5 dex <  log(g f) <  + 0.5 dex grid (in steps of 0.05 dex).