Flicker index α_g as a function of the level of HF noise (black) for the F-star KIC 7940546. The first value, computedfrom raw Kepler observations, is indicated by the red dot and corresponds to α_g = 1.23 and σ_W = 69 ppm. The gray line shows the interpolated function (see Eq. (5)), for which we obtained a quality factor of R² = 0.96. The interpolated index at σ_W = 30 ppm is α_g = 1.69 (blue triangle).