26 should be the serial number of Tibetan literature, HCW is the author's pinyin initials (foreign books are the author's initials), and the call number of the national map generally has three lines, the first line is the cataloging year, the second line is the classification number, and the third line is the author number or serial number. The way to find books is similar. First, find the corresponding bookshelf according to the classification number, then find the cataloging year, and then search according to the title.