[ntp:questions] ntpd -q and driftfile

unruh unruh at wormhole.physics.ubc.ca
Wed Mar 23 06:12:17 UTC 2011

On 2011-03-23, Hal Murray <hal-usenet at ip-64-139-1-69.sjc.megapath.net> wrote:
>>> oh, come off it. Your reaction time is nowhere near what ntp -q would
>>> give you. Using ntp -q run once every hour, and assuming say a 20PPM
>>> drift for the crystal, his clock would be out by less than a 100 ms due to the
>>> drifting, and your reaction time with your watch ( and wyour watch) are
>>> nowhere near that accurate. 
>>Actually, it is on the borderline of the achievable.  You phase lock 
>>your finger bounces to the second ticks and just go that little further 
>>on the exact time.  It's certainly good to 200ms and possibly good to 100ms.
> That would be a fun project for a science fair.
>   Build a setup.  Collect a lot of data.
>   How much does it vary?  For one person, between people, ...
>   How close can you get if you are trying to set a clock?
>     Can you calibrate the person and subtract off a constant?
>     What if you get multiple samples?
> Many years ago, my boss did that sort of stuff.  I think he said that
> normal reaction time from light-on to button-press  was 250 ms.  It's
> faster if there is no penalties for false presses.

You can probably do better than that. That is for the reaction to
something that you do not expect. Ie, you have decide that the event has
occured and then send the messages to your finger to press. However for
the timing, you know exactly when it is going to occur. You can get
yourself into a rhythm on each second, and then finally press the
button. So I suspect you can do about .1 sec if you try hard. 

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