Quadratic orbital solution for V393 Car. Upper panel: O–C diagram for the main pulsation mode of V393 Car in seconds. The best-fit LTTE solution with a quadratic baseline (O–C)quad (Eq. (7)) is overplotted as a continuous cyan line (see Sect. 3 for details). The quadratic baseline a₀ + a₁t + a₂t² is plotted separately as a dashed orange line. The nominal error bars (~0.16 s on average) are smaller than the point size. Lower panel: residuals from the best-fit model in seconds.