Monte Carlo experiments on HiCAT to validate the independent segment error budget shown in Fig. 11, calculated from the experimental PASTIS matrix with Eq. (12) for target contrasts of Δc_t = 5 × 10⁻⁷ (top) and Δc_t = 3 × 10⁻⁷ (bottom). Left: time series of the measured random contrasts (blue), from which the intermittently measured un-aberrated contrast drift (green) has been subtracted. The total duration of each experiment is 65 min and captures 1000 randomly generated WFE maps. The target contrast of both experiments is indicated by the dashed orange lines. Right: contrast measurement from the random WFEs to the left, plotted as histograms. The experimental distributions have a mean (dashed-dotted red lines) of 5.12 × 10⁻⁷ (top) and 3.04 × 10⁻⁷ (bottom). The expected standard deviations (dotted orange lines) as calculated by Eq. (9) are 1.2 × 10⁻⁷ (top) and 6.7 × 10⁻⁸ (bottom), versus the experimentally measured standard deviations (dotted red lines) of 1.3 × 10⁻⁷ and 7.7 × 10⁻⁸.