Highly evacuated electron tube with focusing electron gun and fluorescent screen inclined relative to the beam axis so that the path of the beam can be seen and the effects of electric and magnetic fields can be studied. The electron beam can be deflected using two methods: 1) electrically using electric field of the built-in plate capacitor, or 2) magnetically using external Helmholtz Coils D (U191051). Also determine the fundamental electron charge-to-mass ratio (e/m) and study mean electron velocities using field cancellation.