Cal. Gov. Code § 9356.21
Each member or former member who has 10 years of credited service in this system shall receive credit for active service of not less than one year in the armed forces of the United States, or continuous active service of not less than one year in the Merchant Marine of the United States prior to January 1, 1950, which service was rendered prior to assuming for the first time a state office for which membership in the system was elective and terminated with a discharge under other than dishonorable conditions; provided, however, that the credit to be given for that service shall be on the basis of one year of credit for each five years of credited service in this system, but shall not exceed a total of four years regardless of the number of years of either that service or subsequent service in this system. However, any member or retired former member electing to receive a credit for such military service shall contribute in lump sum or by installments over such period and subject to such minimum payments as may be prescribed by regulations of the board, at the member's contribution rate at the time of election or the retired person's contribution rate at retirement applied, respectively, to the average annual compensation of the member over the three years immediately preceding the election or the average annual compensation of the retired person over the three years immediately preceding retirement.
Military service credit shall not be granted for any military service to which any of the following apply:
An election by a member with respect to military service under this section may be made only while the member is in this system.
Any resulting increase in the allowance of a retired former member shall be applied prospectively only.
Ca. Gov. Code § 9356.21