digital watch vs metronome

digital watch

noun
  • A watch, usually electronic, that displays time in the form of numbers, rather than by a dial and hands. 

metronome

noun
  • A device, containing an inverted pendulum, used to mark time by means of regular ticks at adjustable intervals; an electronic equivalent that emits flashes. 

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