In many pension benefit plans, the employee's compensation determines the amount of his or her contribution or the retirement benefit to which he or she is entitled.

(a) Where the employee's rate of compensation must be calculated to determine pension entitlement, the calculation must be made using the rate of pay that the employee would have received but for the period of uniformed service.

(b)

(1) Where the rate of pay the employee would have received is not reasonably certain, such as where compensation is based on commissions earned, the average rate of compensation during the 12-month period prior to the period of uniformed service must be used.

(2) Where the rate of pay the employee would have received is not reasonably certain and he or she was employed for less than 12 months prior to the period of uniformed service, the average rate of compensation must be derived from this shorter period of employment that preceded service.