In comparing the disability retirement allowance and the service retirement allowance as required by RCW 41.26.130(3), the department must:

(1) Compute the service retirement allowance using a final average salary calculated as follows:

(a) The department shall first calculate the greatest basic salaries that were or would have been payable to such member during any consecutive twenty-four month period within such member's last ten years of service for which service credit is allowed;

(b) The department shall then divide the total basic salaries during the selected twenty-four month period by twenty-four to compute the final average salary.

(2) Compute the service retirement allowance. The service retirement allowance does not include any cost-of-living increases that would have been granted if the service retirement allowance had been in effect during the period of disability retirement.

(3) Compare the service retirement allowance to the monthly disability retirement allowance that the member was receiving on the date that the disability ceased.