Note that the Ultrastable Oscillator they use for their 30 MHz frequency reference has a short term stability of 1 part in 10 trillion! To compare, TCXOs used in commercial circuitry often have a stability of around 1 part per million.
A couple more comments are available on the submission from 3 days ago: <a href="https://news.ycombinator.com/item?id=9890476" rel="nofollow">https://news.ycombinator.com/item?id=9890476</a>