A series of electrodes will be used to build the dynamic ExB-filter, key element of the PTOLEMY concept [1] , and to generate the final retarding potential to adjust the energy of the electrons before the active measuring device. Thus, the voltage stability of those electrodes will directly affect the absolute energy scale and the final energy resolution (sE~ 0.05 eV).
For the reasons mentioned above a special High Voltage (HV) system with unprecedented stability features and with a peculiar voltage monitoring device needs to be developed. The latter is dictated by the fact that any resistive device would affect significantly the voltage we aim at measuring.