proper left vs proper right

proper left

noun
  • The direction which is to the left from an object's perspective, the direction 90 degrees counter-clockwise from the front. 

proper right

noun
  • The direction which is to the right from an object's perspective, the direction 90 degrees clockwise from the front. 

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