def allval(self):
        """Convert the last value to zero. This form represents the entire higher summary level at the granularity
        of the lower  summary level. For example, for a county, it means 'All counties in the state' """

        d = dict(self.__dict__.items())
        d['sl'] = self.sl

        d[self.level] = 0

        cls = self.get_class(self.sl)

        return cls(**d)
Convert the last value to zero. This form represents the entire higher summary level at the granularity
        of the lower  summary level. For example, for a county, it means 'All counties in the state'