oblique mark vs slant line

oblique mark

noun
  • Synonym of slash ⟨/⟩, sometimes (generally proscribed) inclusive of similar marks such as the backslash ⟨\⟩. 

slant line

noun
  • Synonym of slash ⟨/⟩. 

How often have the words oblique mark and slant line occurred in a corpus of books? (source: Google Ngram Viewer )