notebook vs writing pad

notebook

noun
  • A book in which notes or memoranda are written. 

  • A kind of user interface in literate programming, allowing calculations to be interspersed with human-readable comments, diagrams, etc. 

writing pad

noun
  • A collection of blank pages of writing paper, bound together, often with a cardboard cover 

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