felt-tip pen vs permanent marker

felt-tip pen

noun
  • A pen that holds quick-drying ink conveyed to a writing surface by means of a felt nib. 

permanent marker

noun
  • a type of felt-tip pen used to create permanent water-resistant writing on a surface such as a writable DVD 

How often have the words felt-tip pen and permanent marker occurred in a corpus of books? (source: Google Ngram Viewer )