How accurate is world time?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by wisp</i>
<br />Atomic clocks around the world (including the GPS) agree on a time which is accurate to about 1nS per day.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">+/- 1 ns in epoch and 1 ns/day in rate.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">I think I read on a past forum message that the system has to be adjusted daily because of unknown errors of about 0.9nS. Does anyone know if this is correct?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The corrections are made on a clock-by-clock basis as needed by comparing to the U.S. Master Clock. These very small corrections are fairly random in direction, and represent clock noise at the limits of their time-keeping ability.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Can world times achieve accuracies better than this?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Yes, easily, using hydrogen masers and some of the newer clock types that are even more accurate. But all the GPS clocks in orbit are cesiums and rubidiums, at least as of a few years ago. -|Tom|-

Tom

The feedback is very helpful.

I received this reply from another forum, and it also was helpful:
<i> tycho.usno.navy.mil/clocks.html

says that the USNO master clock rate does not vary by more than .1 nanoseconds (100 picoseconds) per day.

I don't think we can disseminate time this accurately over large distances, though.

GPS time dissemination is one of the more accurate available methods, but it's only good to somewhere around 100ns or so from what I've read. This seems a bit conservative to me though, it's equivalent to 100 ft accuracy in position.</i>

Thank you.


wisp

- particles of nothingness

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by wisp</i>
<br />GPS time dissemination is one of the more accurate available methods, but it's only good to somewhere around 100ns or so from what I've read. This seems a bit conservative to me though, it's equivalent to 100 ft accuracy in position.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">That was before SA (signal encryption) was removed in 2000. These days you no longer need a $50K military receiver to get full accuracy from GPS. -|Tom|-