[time-nuts] Visual clock comparison

Bill Hawkins bill at iaxs.net
Sat Apr 18 02:42:59 EDT 2015

IIRC, automobile driver's stopping distance includes 200 msec to process
the need to stop.
Our wetware is not particularly fast.

Bill Hawkins

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Chris
Sent: Saturday, April 18, 2015 12:51 AM
To: time at patoka.org; Discussion of precise time and frequency
Subject: Re: [time-nuts] Visual clock comparison

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
> 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
> 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
> line). However NRC "Talking Clock" could be routed via Satelite which
> compromise the "reading" a little bit. Thanks !
> --
> WBW,
> V.P.

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