@abc.abstractmethod<EOL><INDENT>def get_time_graded(self):<DEDENT>
return<EOL>
Gets the time the gradeable object was graded.

        :return: the timestamp of the grading entry
        :rtype: ``osid.calendaring.DateTime``
        :raise: ``IllegalState`` -- ``is_graded()`` is ``false`` or ``is_derived()`` is ``true``

        *compliance: mandatory -- This method must be implemented.*