code: def _adjust_ser_count(self, plotArea, new_ser_count):
          
          ser_count_diff = new_ser_count - len(plotArea.sers)
          if ser_count_diff > 0:
              self._add_cloned_sers(plotArea, ser_count_diff)
          elif ser_count_diff < 0:
              self._trim_ser_count_by(plotArea, abs(ser_count_diff))
docs: Adjust the number of c:ser elements in *plotArea* to *new_ser_count*.
          Excess c:ser elements are deleted from the end, along with any xChart
          elements that are left empty as a result. Series elements are
          considered in xChart + series order. Any new c:ser elements required
          are added to the last xChart element and cloned from the last c:ser
          element in that xChart.