Closeup of Mk. 1, the first caesium atomic clock from the National Physical Laboratory (NPL) in London from 1955, here at display in the Science Museum in London.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/30661871@N03">Richard Ash</a>
CC BY-SA 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/30661871@N03/20845609130/">IMG_3273</a>