可以参考这个链接
https://www.biblio.com/book-collecting/basics/what-is-a-number-line/#:~:text=Also%20known%20as%20a%20%E2%80%9Cprinter%E2%80%99s%20key%E2%80%9D%20or%20%E2%80%9Cpublisher%E2%80%99s,generally%20indicates%20the%20printing%20of%20that%20particular%20copy.
大体来说是一种记录印次的数字串
https://www.biblio.com/book-collecting/basics/what-is-a-number-line/#:~:text=Also%20known%20as%20a%20%E2%80%9Cprinter%E2%80%99s%20key%E2%80%9D%20or%20%E2%80%9Cpublisher%E2%80%99s,generally%20indicates%20the%20printing%20of%20that%20particular%20copy.
大体来说是一种记录印次的数字串