[ntp:questions] Re: Good GPS for attic?

David Schwartz davids at webmaster.com
Sat Feb 12 00:53:37 UTC 2005

<web1000 at shaw.ca> wrote in message 
news:1108154117.744445.33070 at g14g2000cwa.googlegroups.com...

> how about getting the atomic clock time via internet?
> Matt

    Sadly, this doesn't really work. The problem is that to request the 
time, you have to send out a request and then wait for a reply. Unless the 
request takes exactly as long to get to the clock as the reply takes to get 
back, you have no idea what to do with the time when you receive it.

    Say you send out a request for the time and get a reply 30 milliseconds 
later. The time in the reply was correct sometime between when you received 
it and 30 milliseconds before that. You can 'guess' 15 milliseconds, 
assuming it took as long for the query to get to the clock as it took the 
reply to get to you, but this is no more than a guess. Your time can be as 
much as 15 milliseconds off.


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