Get BMIPR as a time series.

def timeseries(self, dataframe=False):
        """Get BMIPR as a time series."""

        closed_timeseries = self.closed.timeseries(dataframe=dataframe)
        opened_timeseries = self.opened.timeseries(dataframe=dataframe)
        return calculate_bmi(closed_timeseries, opened_timeseries)