[ntp:questions] Visual clock display?

Chris Albertson albertson.chris at gmail.com
Mon Aug 27 02:57:07 UTC 2012

On Sun, Aug 26, 2012 at 7:31 PM, Kennedy, Paul <P.Kennedy at fugro.com.au>wrote:

> Chris Albertson <albertson.chris at gmail.com> wrote:
> > The limit of accuracy of the visual clock is the refresh rate of the
> > monitor.   One the old CRT monitors there was a vertical sync that ran
> at
> > about 60 to 100 Hz.  I think LCDs have something like this too.   You
> can
> > do better than 100 mSec using your method.  In fact it can approach
> > the vertical sync limit.
> 100ms is just fine for me, I think. I don't know how much the console
> driver or a GUI layer adds.
Pretty much what I wrote above.  The limit is the screen refresh time.  The
software and GUI layers are basically "nothing" compared to the 100Hz

So the GUI write to the large RAM buffer inside the video card.  It can do
this very fast.  But the data sits in that buffer untill the next time the
screen needs t be redrawn.  It can sit in there 8 or 12 milliseconds.
There are some other milisecond level delays but it all is less then human
reaction times.      To place this in persective the delay in total is
about what you experience when someone talks to you from across the room
and their voice is delayed 25 or 30 milliseconds by the speed of sound
which is about 1mSec per foot.  You don't notice untillthe distance is
about 50 feet.    In other words don't worry to much about all of this.

Chris Albertson
Redondo Beach, California

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