The total integer number of data points appearing in the series of
        this chart that are prior to *series* in this sequence.

def data_point_offset(self, series):
        """
        The total integer number of data points appearing in the series of
        this chart that are prior to *series* in this sequence.
        """
        count = 0
        for this_series in self:
            if series is this_series:
                return count
            count += len(this_series)
        raise ValueError('series not in chart data object')