Tu indicates that this book belongs to architecture, the first' 8' means "building equipment" under architecture, 3 means air conditioning, heating and ventilation equipment under it, and 2 means heating equipment ... indicating that this book is about building heating equipment (TU832 is all books on this subject).

What does the last missing' 8' mean? I think this is a wrong hand. According to the rules, there is usually a dot between every three numbers.

The meaning of T 1 has not been found, which is related to the cataloging rules of the library where the book is located.