Knowledge: the main elements of the equipment procurement contract. The seller shall properly pack the contract equipment to meet the needs of the contract equipment to be transported to the construction site and stored in the construction site; according to the characteristics of the contract equipment and the different requirements of transportation and storage, the seller shall clearly mark on the packing box, "Carefully and gently," "This end is facing upward, do not turn upside down. ", "Keep dry" and other appropriate markings. For oversized and overweight parts as agreed in the special contract terms, the seller shall mark the "center of gravity" and "lifting point" on both sides of the box to facilitate loading, unloading and handling. If the shipment contract equipment contains flammable and explosive substances, corrosive substances, radioactive substances and other dangerous goods, should be marked on the packing box dangerous goods sign.