Grantee of the franchise shall during the term thereof pay to city a sum annually which shall be equivalent to two percent of the gross annual receipts of grantee arising from the use, operation, or possession of the franchise; provided, however, that such payment shall in no event be less than a sum which shall be equivalent to one percent of the gross annual receipts derived by grantee from the sale of gas within the limits of city under the franchise and the constitutional franchise. (Prior code § 10-28)