Grantee shall, during the term for which this franchise is granted, pay to said county two percent of the gross annual receipts of applicant arising from the use, operation, or possession of the franchise; provided, however, that such payment shall in no event be less than one percent of the gross annual receipts of applicant derived from the sale within the limits of the county of the utility services for which the franchise is awarded. Such percentage shall be payable annually from the date of the granting of the franchise, and if such payment shall not be made, such franchise shall be forfeited. The method of computing said payment shall be in accordance with that laid down by the Supreme Court of the state of California in its construction of the foregoing language, and any future modification of such method set forth in any decision of the Supreme Court hereafter rendered shall supersede the method prior to such decision.