The drift and jump of EEL spectra or images can be induced by different reasons:
        i) Induced by charging as a result of the exposure to the electron beam:
        i.a) The EEL spectrum or image first gradually drifts in one direction when the charge is building up;
        i.b) It suddenly jumps in the opposite direction when the charge dissipates with a discharge.
If something is really charging, then increasing the beam current while keeping the illuminated area on the viewing screen the same should lead to an increased rate of drift. A small selected area diffraction (SAD) aperture can be used in order to determine whether the charging occurs in the camera chamber or in the GIF. The small SAD aperture ensures that all the electrons enter the GIF and none can hit and charge any parts in the camera chamber. If the charging continues, then it must be in the GIF. Otherwise, it should be in the camera chamber if it stops.
        ii) Induced by unstable high voltage of the electron beam.

To know whether the energy-selecting slit is charging or not, we can move the slit edge to the screen under electron-exposure. If the slit is charging, then we may observe:
         i) The EEL spectrum or image first gradually drifts in one direction when the charge is building up.
         ii) It will suddenly jumps in the opposite direction when the charge dissipates with a discharge.