@abc.abstractmethod<EOL><INDENT>def get_num_minutes(self):<DEDENT>
return<EOL>
Gets the number of minutes in an hour.

        For a variable minute time system, the number of minutes defined
        is returned. If there are no "minutes" in this time system then
        this value may be zero. If there are no "hours" defined then the
        number of minutes is the number of minutes in a day.

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


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