Accuracy of estimating the NIV by integrating periodograms of simulated eROSITA-like pink-noise light curves. Unlike in Fig. A.1, the NIV is estimated here by subtracting both the Poisson and fractional-exposure noise, using Eqs. 16, and 17, with parameters listed in Table 4 from the periodograms. This figure shows the relationship on both a logarithmic (top panel) and a symmetric logarithmic (lower panel) scale, to showcase how close the individual NEVi measurements are to the NIV, as well as the complete range of values measured for NEV_i.