[time-nuts] Is there a good web page introducing ADEV?

[Mod Mix]

I found http://www.leapsecond.com/pages/adev/ being pretty helpful to 
get the concept.
Best, Ulli

Am 24.09.2020 um 21:35 schrieb Tom Van Baak:
> Hi Hal,
>
> ADEV turns out to be pretty hard to understand. I took me years for it 
> to sink in. There are web pages, articles, even books. Part of the 
> problem is matching the explanation with the audience.
>
> It's hard to take a clock phase / frequency / measurement example and 
> use it to teach people who want to use ADEV for stock market or 
> climate analysis. It's hard to take quartz and atomic clock examples 
> and use it to teach a mechanical clock & watch audience. Another 
> example is applying ADEV to sensor noise [1]. Even though it is 
> technically correct it's not likely to help explain the guts of a 
> GPSDO or NTP.
>
> I can point you to a list of references but in my experience they are 
> too shallow or way too deep. What you want is something specific to 
> your NTP case. How about ignoring ADEV completely. Maybe just try to 
> explain why there is polling, why there is a poll interval, how the 
> poll interval could be less or more, why that may or may not affect 
> performance, how it might improve performance, or why it might 
> actually make it worse. That gets the concept of the "cross-over 
> point" across without all the rest of ADEV baggage.
>
> Another challenge is that an audience needs to unlearn what they were 
> taught in school. We were told: the more data the better; the more 
> data the more precision you get; averaging data always gives better 
> results; get rid of outliers; stuff like that. Those lessons are valid 
> for measurements of something that doesn't change. But they are not 
> valid if what you're measuring is changing *while* you are making all 
> those measurements. Hence the ADEV "V" you mentioned. So maybe try to 
> explain NTP using words and analogies rather than using heavy math and 
> statistics; try not mentioning ADEV, slopes, and power law noise at all.
>
> /tvb
>
> [1] https://www.phidgets.com/docs/Allan_Deviation_Primer
>
>
> On 9/23/2020 5:26 PM, Hal Murray wrote:
>> I'm looking for something for non-nuts, the general idea without any
>> complicated math.
>>
>> Deep in ntpd is logic to adjust the polling interval, attempting to 
>> find the
>> bottom of the V.  It's hard to describe that to somebody who doesn't 
>> know
>> about ADEV.
>>
>>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to 
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.