Cal. Food & Agric. Code § 55581

If any farm product is sold to and purchased by any processor on the basis of weight, such product shall be weighed by a weighmaster licensed under the laws of this state, and a certificate as to such weight issued by him shall be delivered to the seller by the processor or by the weighmaster as agent for the processor. Settlement for such product shall be made on the basis of the weight which is shown on the certificate.