def METHOD_NAME(
    *, ureg: UnitRegistry, correct_ans: str
) -> Callable[[str], Tuple[bool, Optional[str]]]:
    """Returns the grading function used for units only grading mode."""
    parsed_correct_ans = ureg.Quantity(correct_ans)
    def grade_only_units(submitted_ans: str) -> Tuple[bool, Optional[str]]:
        parsed_submission = ureg.Quantity(submitted_ans)
        if parsed_correct_ans.units == parsed_submission.units:
            return True, None
        return False, INCORRECT_FEEDBACK
    return grade_only_units