California Code, Government Code - GOV § 20637

“Compensation earnable,” with respect to a state member receiving supplemental payments pursuant to Section 21160 at the time of retirement or death, means the highest average monthly compensation paid to the employee in the classification in which the member was employed at time of becoming eligible for benefits pursuant to Section 21160, or the average compensation earnable by the member at time of retirement or death, whichever is higher.