Looking at the Thunderbolt manual, I came across this: <quote> It is important to remember that any real-time UTC is actually a prediction of UTC. The official UTC time is published approximately one month after the fact. </quote> It makes sense that real-time "UTC" is a prediction, since UTC is the average of a number of clocks around the world, we can't know ahead of time what they are going to do, we can only guess. However, it is amazing to me that it takes a month to have the official time, which I guess is published in the form of an error from the predicted number. That reminds me when Motorola went after the Malcolm Baldridge award, they looked at their processes and someone noticed that while FedEx could deliver a piece of paper or hardware across the country overnight as long as you call them before 4:00 PM, it took Mot 9 weeks to issue a check for that transaction, which involved many more people than it took to carry the package. Here, we need a month to find out how many nanoseconds we were off... That's a lot of data to keep track off if you actually need the ultimate accuracy. I would not want to be the one counting nS for a month... Didier

In message: <4555CFF8.4030602@cox.net> Didier Juges <didier@cox.net> writes: : Here, we need a month to find out how many nanoseconds we were off... : That's a lot of data to keep track off if you actually need the ultimate : accuracy. I would not want to be the one counting nS for a month... UTC is the realization of time sources from around the world. I don't know if it still takes a month to publish the data, but I do know that the data is accumulated in files, and those files need to be sent to BIPM manually. I believe that there are efforts underway to harmonize the output format of the different timing systems to streamline the process... Warner

> Looking at the Thunderbolt manual, I came across this: > > <quote> > It is important to remember that any real-time UTC is actually a > prediction of UTC. > The official UTC time is published approximately one month after the fact. > </quote> > > It makes sense that real-time "UTC" is a prediction, since UTC is the > average of a number of clocks around the world, we can't know ahead of > time what they are going to do, we can only guess. Didier, Remember it's all a matter of statistics. If you want 1 us or even 100 ns accuracy, it's much closer to "certainty" than a "guess". Any two clocks will drift apart, so time is always a sort of a guess. The key point is not if clocks agree, but how close they will be over some elapsed interval. Hence, the use of statistics like ADEV, or MTIE, etc. In a sense, every clock is a "prediction" and all of timing is a guess. The past and present phase and rate combine to create the future time, to some level of accuracy, with some probability. The measure of how well the past behavior of a clock is a prediction of future time is exactly what the Allan deviation measures. > However, it is amazing to me that it takes a month to have the official > time, which I guess is published in the form of an error from the > predicted number. Like a GPSDO, there is a crossover point where too frequent a correction is either not good or technically not even possible (due to inter-lab measurement noise or clock synthesizer granularity). I'm not sure where that point it; probably less than one month, to be sure. But don't think that updating the rate of the worlds clocks, like, every hour would be a good thing either. /tvb