The trading object of treasury bond futures is virtual bonds, not real bonds. However, at the time of delivery, real national debt must be used. Because the contract stipulates that all treasury bonds with a remaining maturity of 4-7 years can be used for delivery, there are many treasury bonds that meet this condition and the prices are different. Therefore, it is necessary to link these national bonds with the virtual bonds in the transaction, which is convenient for calculation and comparison, a bit like commodity delivery. The latest futures quotation is the latest price of virtual coupons.