Bill A very big thank you for what must be a near perfect (accurate) answer to a question that most of us without Degrees have pondered from time to time. I shall paste this into my "book of many answers"
Regards Roy Phillips. ----- Original Message ----- From: "wje" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; "Discussion of precise time and frequency measurement" <[email protected]> Sent: Tuesday, July 22, 2008 12:03 PM Subject: Re: [time-nuts] Stability vs. Accuracy > Simply put, stability is a measure of how much something varies from a > constant value. > A stable value doesn't mean an accurate value; accuracy is a measure of > how close to some standard value a device emits (in this case) or > measures, for a meter. > > So, you could have something that's perfectly stable but not accurate. > You can also have something that's accurate but not stable. > > In theory, they can be perfectly (ok, nearly perfectly) accurate because > their lack of stability is averaged out over a long period of time, and > the average value is an accurate representation of the time kept by the > satellites, which themselves provide an accurate representation of > 'true', i.e., NIST time. > > In practice they wander around a bit, and that wandering is the > stability measurement you see. What you can tell from the stability > figures is that the unit is that close to perfect accuracy most of the > time. The stability figure is really a measure of the statistical > probability that at any given time the accuracy is within that bound. > > Why do they wander? Many factors contribute, ranging from the stability > and accuracy of the local VCXO and its control loop to atmospheric > propagation variations to variations in the satellite clocks themselves, > etc. > > Bill Ezell > ---------- > They said 'Windows or better' > so I used Linux. > > > > Richard Dabney wrote: >> I'm not a scientist or engineer but have a question to those of you who >> are. >> >> The many recent posts regarding the GPSDOs and comparisons between the >> various ones have been comparing stability. How about accuracy compared >> with the national frequency standard? >> Are stability and accuracy the same? Stability to E-13.5 with the >> Thunderbolt. How close to >> perfect time and frequency?............ Thanks...Dick W5UFZ FMT-nut >> >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
