Cal. Food & Agric. Code § 35163

Every person, except a licensed tester, who takes any sample of milk, cream, or any fluid derivative of milk or cream, which is purchased, received, or sold on the basis of milk fat which is contained in it, on which sample tests are to be made as a basis of payment, and every person who weighs or measures milk, cream, or any fluid derivative of milk or cream, shall hold a sampler’s and weigher’s license if the weight or measure is to be used as the basis of payment.