grading vs rating

grading

noun
  • A rank or grade. 

  • Gradation. 

rating

noun
  • A position on a scale. 

  • An enlisted seaman not a commissioned officer or warrant officer. 

  • An evaluation of status, especially of financial status. 

  • A number, letter, or other mark that refers to the ability of something. 

  • A quantitative measure of the audience of a television program. 

  • A seaman in a warship. 

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