[en] The authors introduce a three step method to optimally bias a photomultiplier obtaining the best performance in single photo-electron counting. Instead of employing an activated spectroscopy which is not easy to repeat condition, the single electron emitting noise was observed to characterize photo multipliers behavior relating to single photo-electron counting. Three parameters were used to detail single electron spectrum shape being advanced than other reported way. This method test the influence of three settings that would affect the spectrum shape