which is the most accurate watch or clock in the world

Question: which is the most accurate watch or clock in the world
- Keywords:
  clock,
  watch,
  world
Asked by aabb266 to Patricia, Kamal, George, Charles, Beatrice on 23 Jan 2017.
- George Githinji answered on 23 Jan 2017:
  
  The oscillation of the caelcium atom are the most accurate. 9 billion such oscillations comprise the standard duration measure of 1 second. Various watches are calibrated to approximate this standard of oscillation.