diagonal mark vs front slash

diagonal mark

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

front slash

noun
  • Synonym of slash ⟨/⟩. 

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