Variances for cross-spectra in EE and BB based on PR4 simulations, including: cosmic (sample) variance (black); analytic statistical noise (red); and PR4 noise from Monte Carlo simulations (green), including noise and systematics with (solid line) or without (dashed line) correction for the transfer function. The sky fraction used here is 80%, as it illustrates well the effect of both systematics and transfer-function corrections (Planck Collaboration Int. LVII 2020).