The so-called mother money is the standard model money produced by the central and local finances when a large number of coins were minted in ancient times. According to the use of mother money as a model, mother money can be divided into three types, namely money sample, carved mother money and cast mother money. The money sample is a physical sample of the coin carefully carved from materials such as tin, ivory or mahogany according to the design of the coin. As for the two calligraphy styles on one coin, the purpose is to submit it to the court for the emperor's approval. Strictly speaking, the money sample cannot be counted as currency, because it is only used as a physical drawing to be submitted for review and approval and cannot be circulated. Coin samples are for the emperor's review. In theory, there should only be one sample of a type of coin, so the quantity is extremely rare and can hardly be seen in the trading market. An obvious difference between mother money and bank money is the size and thickness of the coins. Since coins were struck in ancient times using a mold-casting method, the volume of the produced banknotes would be slightly smaller than the mother coins used as the sample. The size and thickness of mother money are larger than ordinary coins. When collecting mother coins, you should first pay attention to large coins that are larger than ordinary coins, and secondly, pay attention to heavy coins that are different in weight from ordinary coins.