Numerical noise observed in the synthetic observations due to the surface discretisation. Residuals of the synthetic observations for discretisation factors 10, 7, 5, and 3 are displayed in different colours along with their standard deviations σ. The amplitude of residuals for discretisation factor 5 is roughly 2 × 10⁻⁴. This value should be regarded as the precision of the numerical model for this level of surface discretisation. Due to the symmetry of the surface discretisation, only one half of the phase curve is displayed for the sake of clarity.