@abc.abstractmethod<EOL><INDENT>def get_num_seconds(self):<DEDENT>
return<EOL>
Gets the number of seconds in a minute.

        For a variable second time system, the number of seconds defined
        is returned. If there are no "seconds" in this time system then
        this value may be zero. If there are no "minutes" defined then
        the number of seconds is the number of seconds in an hour.

        :return: the number of seconds
        :rtype: ``cardinal``


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