This may be of interest:
http://www.tp178.com/jd/watch-school/1/article1.html

wrote in message
oups.com...
The modern equivalent:
http://www.leapsecond.com/pages/atomic-bill/

I built a real Atomic Watch once, based on a miniature EG&G Rubidium
physics package. The battery pack needed to operate the
temperature-control heater was about the size of a clock-radio.

jw