main line vs old money

main line

noun
  • A standard sequence of opening moves considered to be best play. 

old money

noun
  • The monetary system used in the United Kingdom and Ireland before decimalisation in 1971 and consisting of pounds, shillings, pence and farthings. 

  • The imperial system of measurement, as opposed to the metric system. 

  • Families that have been wealthy for generations or members of such families. 

How often have the words main line and old money occurred in a corpus of books? (source: Google Ngram Viewer )