Possible Clues:

• Reference work, usually
• "Bartlett's Familiar Quotations," e.g.
• Heavy work?
• Book in my direction
• Volume rising in the average motorway
• Thick textbook
• A-B or C-D, e.g.
• Only part of photo meant to be seen in book
• Big reference volume
• It might need two hands to be removed from a shelf