chalkboard vs iPad

chalkboard

noun
  • A slate or enamel board for writing on with chalk; a predecessor to a whiteboard. 

verb
  • To write or draw on a chalkboard. 

iPad

noun
  • Any lightweight low-power tablet computer. 

  • A lightweight low-power tablet computer of a particular range from Apple Inc. 

How often have the words chalkboard and iPad occurred in a corpus of books? (source: Google Ngram Viewer )