@classmethod
def validate(cls, unit):
    """
        Check if the given unit is valid (exists).

        Parameters
        ----------
        unit : unicode
            The unit to be checked.

        Returns
        -------
        None
            If the given unit is valid and exists.

        Raises
        ------
        Unit.UnknownUnitError
        """
    if not any(map(lambda d: unit in cls._units_per_dimension[d], cls.
        _units_per_dimension)):
        raise cls.UnknownUnitError(unit)
