diagonal mark vs fraction bar

diagonal mark

noun
  • Synonym of slash as the forward slash ⟨/⟩ and sometimes also its proscribed sense inclusive of the backslash ⟨\⟩. 

fraction bar

noun
  • The line separating the numerator from the denominator, whether horizontal, (sometimes proscribed) oblique, or diagonal. 

How often have the words diagonal mark and fraction bar occurred in a corpus of books? (source: Google Ngram Viewer )