Each delivery of liquefied petroleum gas on a package basis in tanks, cylinders or containers to consumers and each delivery of liquefied petroleum gas from vehicle tank or other vessel into tanks, cylinders or containers connected to consumer apparatus when sale is based on a quantity so delivered shall be accompanied by a delivery ticket and a duplicate thereof, on which shall be distinctly expressed, in ink or other indelible substance, the net weight or volume of such liquefied petroleum gas delivered together with the name of the seller and the name of the purchaser of such liquefied petroleum gas. One of such tickets shall be surrendered upon demand to the sealer of weights and measures for his inspection. When the sealer desires to retain the customer’s ticket, a delivery slip issued by the seller or his agent shall be delivered upon request to the purchaser, or his agent or representative, of such liquefied petroleum gas and the other ticket shall be retained by the seller. The weight of liquefied petroleum gas and the tanks, cylinders or containers into which it is delivered, sold or stored, when sold by weight, shall be expressed in avoirdupois pounds and the weight determined on scales of approved design and sealed by a sealer of weights and measures. Liquefied petroleum gas shall be sold or offered for sale by avoirdupois weight, liquid measure or cubic foot; provided nothing herein shall be interpreted so as to prohibit the sale of liquefied petroleum gas by other units employed prior to October 1, 1951, by industry and accepted by the trade and approved by the Commissioner of Weights and Measures if the meter or scale and the invoice clearly indicate to the consumer the equivalent of such unit in avoirdupois pounds or fractions thereof. All meters and scales employed in the sale or delivery of liquefied petroleum gas shall be of a type approved by said commissioner.