I was going through my e-mails for some information on atomic frequency standards, when I came across an e-mail that I had sent to Tom Van Baak in 2007 congratulating him for his family-friendly time dilation experiment. If you are not familiar with his work, I heartily recommend that you explore his precision-time-keeping webpage at LeapSecond.com.
Efratom Model M-100 Rubidium Frequency Standard (RFS) oscillators are widely available in the surplus market. Units on eBay commonly sell in the $150 to $200 range. Despite their low surplus price, they were originally very expensive components, with superb performance. The M100 was designed to be used by the military as a master oscillator in high-performance