When choosing a class number, it should represent (as nearly as possible) the primary subject(s) of the material being cataloged, as modified by a topical subheading when appropriate, or, in some cases, by the form or type of material being cataloged. Use the most specific number available.
After assigning the MeSH terms to a work:
Use a broader number if:
If more than one primary subject is considered, choose the class number using the following guidelines: