bellwether vs handbook

bellwether

noun
  • A stock or bond that is widely believed to be an indicator of the overall market's condition. 

  • Anything that indicates future trends. 

  • The leading sheep of a flock, having a bell hung round its neck. 

handbook

noun
  • A place where illicit bets can be placed. 

  • A topically organized book of reference on a certain field of knowledge, regardless of size. 

How often have the words bellwether and handbook occurred in a corpus of books? (source: Google Ngram Viewer )