The magnetic spectrometer is designed to detect low energy electrons (5–50 MeV) with good energy (10%) and angular ( < 5 ∘ ) resolutions, and sufficiently large acceptance ( 10 cm 2 sr ), to monitor short term changes of the trapped particle population in the Earth's magnetic field. The influence of multiple Coulomb scattering is reduced by active collimation, filter planes composed of edgeless silicon microstrip detectors. The incident and exit particle trajectories are reconstructed in four planes of scintillating fibers. The spectrometer is a digital device in the sense that the notion of sampling is omnipresent: at the level of the filter plane design to suppress large angle multiply-scattered electrons, and at the level of the frontend electrons, where silicon photomultipliers (SiPM) are used.