@abc.abstractmethod<EOL><INDENT>def has_variable_hours(self):<DEDENT>
return<EOL>
Tests if this time system has a variable number of hours in a day.

        :return: ``true`` if the number of hours per day varies, ``false`` if the number of hours per day is constant
        :rtype: ``boolean``


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