[time-nuts] Visual clock comparison

Chris Albertson albertson.chris at gmail.com
Sat Apr 18 01:51:05 EDT 2015

It would be an easy experiment to get two analog clocks and put them
side by side.  You would not even have to set them to the "true" time,
just to each other.  Let one run slower and wait until you can see a

Clocks on a computer screen are different because the screen is
refreshed one order of about 100 times per second.  They move in
jumps, not continuously.

Ears are better than eyes at this.  If you choose the "right" tick
sound.  The best one sounds like a drummer hitting the metal rim of
his drum to make a "click" sound.  Some people can hear if two clicks
are just a few milliseconds apart or not.  Beware of the speed of
sound.  It is very slow, about 1 milli sec per foot of distance.  You
clocks must be very close to each other or the delays will be

On Fri, Apr 17, 2015 at 11:16 AM, d0ct0r <time at patoka.org> wrote:
> Hello, Netizens !
> I am wandering what is the average human ability to visually compare two
> clocks ? Let say I have XClock application running on one machine (stratum 1
> NTP) and I have my project clock close by. And I would like to match the
> reading. If I'll see the difference, which range it will be ? 100ms or so ?
> I also tried to use my ears (CHU radio signals and clock display, NRC phone
> line). However NRC "Talking Clock" could be routed via Satelite which will
> compromise the "reading" a little bit. Thanks !
> --
> WBW,
> V.P.
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Chris Albertson
Redondo Beach, California

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