Top: squared visibilities V² observed on Achernar (filled circles and error bars) and computed (opened squares) from the best-fit CHARRON model (Table 6) as a function of spatial frequency (left column) and baseline PA (right column). Bottom: V² residuals from observations relative to the best-fit model in units of corresponding uncertainties. Vertical solid lines indicate the position angles of the visible (216.9° ≡ −143.1°) and hidden (16.9° = 216.9°−180°) stellar poles. The horizontal dotted lines delimit the ± 3σ region around zero (dashed line).