diagonal mark vs forward slash

diagonal mark

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

forward slash

noun
  • Synonym of slash ⟨ / ⟩. 

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