Columbia subject headings:
Occupations--Classification--Handbooks, manuals, etc.
Occupations--United States--Classification--Handbooks, manuals, etc.
Harvard subject headings:
Occupations--Classification--Handbooks, manuals, etc.
Occupations--United States--Classification--Handbooks, manuals, etc.
Princeton subject headings:
Occupations--Classification--Handbooks, manuals, etc.
Occupations--United States--Classification--Handbooks, manuals, etc.