@utilities.arguments_not_none<EOL><INDENT>def set_effective_date(self, date, rate):<DEDENT>
raise errors.Unimplemented()<EOL>
Sets the effective date.

        arg:    date (timestamp): a date
        arg:    rate (decimal): the rate at which the clock should tick
                from the given effective date. 0 is a clock that is
                fixed
        raise:  NullArgument - ``date`` is ``null``
        *compliance: mandatory -- This method must be implemented.*