It is used to guard against theft. When you buy a book in a bookstore and pay for it, the book has to go through a computer test. Now all bookstores have electronic security doors. If you take out the book without paying, it will ring when you walk to the electronic security door. This metal bar is working, which affects the ultraviolet ray of the electronic door, and then the person in charge of the bookstore will catch you. After payment and computer test, the computer will send the test information of the book to the electronic security door. The certificate has been paid and will not ring. You can go safely.
Generally, science and education books are ordered regularly by the Education Bureau after the school organizes students to pay fees, and will be distributed to students by the school after the school starts, so it is not necessary.