Impact of using an approximate solar modulation, illustrated by the calculation of (¹⁰Be/⁹Be)^TOA/(¹⁰Be/⁹Be)^IS as a function of the kinetic energy per nucleon. Top panel: TOA-to-IS ratio for the exact calculation with USINE (solid blue line) or using the approximate modulation Eqs. (13)–(15) with Eq. (12) for the energy dependence of the ⁹Be IS flux (dashed black line). The grey lines show the broken-down corrective terms entering Eq. (13). Bottom panel: relative difference between the approximate calculation and the exact calculation. The range highlighted in yellow corresponds to the region where the AMS-02 and HELIX experiments should measure ¹⁰Be/⁹Be.