A timely explanation (with lots of precision)

I realize now that I might have came across as a very cryptic scientist after my last post, where I showed an instrument set-up in our lab and a note that our boss left us. I do believe that it is our duty as scientists to make our research available and share our findings and do our best to try to explain how we came to whatever point in our research that we are trying to present, what's the point of figuring out the secrets of the universe if we are going to keep them to ourselves?! I'm going to explain to you what you saw on that picture and what is the meaning of that note from our beloved leader and mentor, John Willison.

What you saw on the picture are six precision clocks, the technical name is GPS disciplined oscillator, GPSDO, yes GPS, as your car's GPS, same thing. The company calls them FS740's (as John refers to them in the note) and they are our latest product. They are almost ready to hit the street. One of the last experiments that we are carrying out with these six prototypes is to observe and measure how close in time any given pair of clocks are. The set-up is simple, connect source and inputs of the units and set them up to read each other time output, each clock measuring how close it thinks it is to the clock they it is observing. You can do this varying the time of observation and you can even give it a number by calculating the Allan deviation of the two clocks. Wait, what is the Allan deviation of two variables as a function of observation time? It is an statistical estimate of how close two clocks will be after a certain observation time. An Allan deviation that goes to zero over time means that the two clocks compared are in sync. This concept applies to so many other situations in physics. Want to know more? I can't recommend it enough, if you are interested in precision timing, join Time Nuts, a wonderful community of experts started by Tom Van Baak. Visit Leapsecond.com and sing up for the mail list.

The picture you see heading this post is the result of measuring the Allan deviation (or Sigma-Tau, just another name) of three pairs of FS740s, each pair with a different time bases. This is the data that John read on the instruments when he left that note. Let me explain what each point in that graph means. Let's pick one, Sima-tau at 1 second of a Rubidium based GPSDO, the graph shows 1.8e-11, this means that one clock will be off in time by a 18 parts per trillion (that's 12 orders of magnitude!) after one second from the other clock.

I don't want to scare you with anymore technicalities, I get scared myself! But if this article makes you want to know more about precision clocks and the beautiful physics behind them, and most importantly how they can help us reach new horizons in terms of better technology, more precise, more robust, then I'll have achieved my goal.