Cal. Gov. Code § 20631

A contracting agency may report an amount for each member that is equal to a uniformly applied percentage of salary in lieu of computing and reporting the actual compensation attributable to each individual member if the contracting agency has agreed in a memorandum of understanding reached pursuant to Chapter 10 (commencing with Section 3500) of Division 4 of Title 1 that the aggregate amount to be reported by the contracting agency for all members within a membership classification bears a reasonable relation to the aggregate amount that would otherwise be required to be reported pursuant to Section 20636.