[time-nuts] PC time app

Hal Murray hmurray at megapathdsl.net
Sat Nov 26 02:30:01 EST 2011


> I'm curious as to what folks are doing with PC's that require micro second
> accuracy for days or weeks or what have you.

> Any examples? 

The obvious one is you can be a real time nut.  :)

With a good clock, you can measure network delays.

The normal way that ntp works is to exchange packets with a server.  That 
gives you 4 time stamps:
   the time the request left the client
   the time the request arrived the server
   the time the response left the server
   the time the response arrived the client
ntp assumes the network delays in each direction are the same and adjusts the 
local clock to get that answer.  (that's after lots of filtering and such)

If instead, you assume that both clocks are good, you can directly calculate 
the transit time in each direction.

If you are going 1000 miles, 1 ms accuracy is probably good enough.  If you 
are interested in LAN distances you probably need better than that.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.







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