pendulum vs stopwatch

pendulum

noun
  • A body suspended from a fixed support so that it swings freely back and forth under the influence of gravity, commonly used to regulate various devices such as clocks. 

  • A watch's guard-ring by which it is attached to a chain. 

  • Used to refer to the tendency of a situation to oscillate (between two extremes). 

  • A lamp, etc. suspended from a ceiling. 

stopwatch

noun
  • A timepiece designed to measure the amount of time elapsed between a particular time when activated and when the piece is deactivated. 

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