Cosmic ray electron spectrum measured by HESS using two different analysis chains reported by Kerszberg et al. (2017), Kerszberg (2017), Kraus (2018). Black thick dotted line shows the residual charged cosmic ray background expected in CTA (Maier 2019). Grey shading shows the residual background level in Fermi/LAT (Neronov & Semikoz 2020). Dashed grey lines with numerical markers show the flux levels from 10⁻⁶ to 10⁻³ of the cosmic-ray all-particle flux. The dotted thin grey curve shows the calculation of the residual cosmic-ray nuclei background in the HESS electron flux analysis reported by Kraus (2018). The green dash-dotted line shows the spectrum of the atmospheric neutrino background in neutrino telescopes (Aartsen et al. 2015). The thick grey solid line shows the sum of the best-fit model of the cosmic ray electron spectrum and the residual cosmic ray nuclei background suppressed by a factor 10⁶.