28.5.3. For the purposes of this plan and Title IV of the Act respecting the Government and Public Employees Retirement Plan (chapter R-10), the pensionable salary for the years or parts of a year covered by the agreement is the salary the teacher would have received or, for a period in respect of which salary insurance benefits apply, the salary which he would have been entitled to receive if he had not availed himself of this division. The service credited is the service that would have been credited to the teacher if he had not availed himself of this division.