In all cases where scrap metal and salvage materials are purchased or sold by dealers, brokers, or commission merchants on the basis of weight or measure, the quantity of the scrap metal and salvage material shall be determined by a weighmaster, and a weighmaster certificate shall be issued to the seller and buyer. Settlement for the materials shall be made on the quantity shown thereon. If the quantity indications are readily accessible and clearly readable to both the buyer and seller, at the time of determination, a weighmaster certificate is required to be issued only when requested by the buyer or seller.