Knowledge point: the main content of equipment purchase contract. The seller shall properly package the contract equipment to meet the needs of transportation and storage of the contract equipment at the construction site; According to the characteristics of the contract equipment and the different requirements of transportation and storage, the seller shall clearly mark the packing box with appropriate marks such as "handle with care", "This end is upward, please do not turn upside down" and "keep dry". For oversize and overweight parts agreed in the special contract terms, the seller shall mark "center of gravity" and "lifting point" on both sides of the packing box for easy loading, unloading and handling. If the shipped contract equipment contains inflammable and explosive substances, corrosive substances, radioactive substances and other dangerous goods, the dangerous goods sign shall be marked on the packing box.