docs: 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)