on which the member terminates employment or otherwise ceases to be a member, the portion of the pension benefit attributable to employment after the commencement of section 35 of the Act shall be the difference obtained by deducting from the pension benefit, the pension benefit calculated in accordance with the provisions of the plan and with the years, including parts of a year, of employment credited to the member under the plan before the commencement of section 35 of the Act, using the rate of remuneration of the member as of the date of termination of employment or cessation of membership or the average of the rates of remuneration of the member over the specified or limited time period, as the case may be.