docs: def get_uncertainty(self, name=DEFAULT, direction=None, **kwargs):
          """ get_uncertainty(name=DEFAULT, direction=None, default=None)
          Returns the *absolute* up and down variaton in a 2-tuple for an uncertainty *name*. When
          *direction* is set, the particular value is returned instead of a 2-tuple. In case no
          uncertainty was found and *default* is given, that value is returned.
          """
          if direction not in (None, self.UP, self.DOWN):
              raise ValueError("unknown direction: {}".format(direction))
  
          unc = self.uncertainties.get(name, *kwargs.values())
  
          if direction is None:
              return unc
          else:
              return unc[0 if direction == self.UP else 1]