ballpoint pen vs pencil case

ballpoint pen

noun
  • A pen, similar in size and shape to a pencil, having an internal chamber filled with a viscous, quick-drying ink that is dispensed at the tip during use by the rolling action of a metal sphere (around 0.7 mm to 1 mm in diameter). 

pencil case

noun
  • An object purposed to contain different stationery like pencil, rubber, correction fluid, etc. 

How often have the words ballpoint pen and pencil case occurred in a corpus of books? (source: Google Ngram Viewer )