@property
    def _values_ref(self):
        return "Sheet1!$%s$2:$%s$%d" % (
            self._col_letter, self._col_letter, len(self._values)+1
        )
The Excel worksheet reference to the values for this series (not
dataset/ETHPy150Open scanny/python-pptx/pptx/chart/data.py/_SeriesData._values_ref