NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: NIST website time accuracy
From: Lu Abel
Date: 2010 Jul 25, 09:28 -0700
From: John Karl <jhkarl@att.net>
To: NavList@fer3.com
Sent: Sat, July 24, 2010 6:19:42 PM
Subject: [NavList] NIST website time accuracy
From: Lu Abel
Date: 2010 Jul 25, 09:28 -0700
As explained by another post, they measure the round-trip delay and compensate the delay for that. Sometimes when I've logged into www.time.gov, I've seen "accurate to" listings higher than 0.2 seconds. I strongly suspect that that's because they're not seeing a constant delay to your computer, but rather one that jumps around.
I'd also point out that transmissions from WWV and its siblings also suffer from time delays -- but they can't be measured because there's no way for the receiver to transmit information back to WWV, the way NIST's internet time service can.
Net-net I suspect that www.time.gov is probably about the most accurate time standard one can get short of a GPS receiver (which, as people pointed out on posts a year or two ago, can have their own problems). And in any case, more than adequately accurate for celestial navigation.
Lu Abel
I'd also point out that transmissions from WWV and its siblings also suffer from time delays -- but they can't be measured because there's no way for the receiver to transmit information back to WWV, the way NIST's internet time service can.
Net-net I suspect that www.time.gov is probably about the most accurate time standard one can get short of a GPS receiver (which, as people pointed out on posts a year or two ago, can have their own problems). And in any case, more than adequately accurate for celestial navigation.
Lu Abel
From: John Karl <jhkarl@att.net>
To: NavList@fer3.com
Sent: Sat, July 24, 2010 6:19:42 PM
Subject: [NavList] NIST website time accuracy
The U.S. National Institute of Standards & Technology (NIST) quotes a 0.2 second accuracy for their animated clock on their website http://nist.time.gov/timezone.cgi?Central/d/-6/java.
Given the vagaries of internet transmission times, can anyone tell me how they do this??
John
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