[time-nuts] Changing ADEV, (was Phase, One edge or two?)

Bob Camp kb8tq at n1k.org
Sat Oct 25 17:45:08 EDT 2014


Hi

> On Oct 25, 2014, at 4:08 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 
> Bob,
> 
> On 10/25/2014 08:54 PM, Bob Camp wrote:
>> Hi
>> 
>>> On Oct 25, 2014, at 2:18 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>>> 
>>> 
>>> 
>>> On 10/25/2014 07:06 PM, Tom Van Baak wrote:
>>>>> In the case of the TimePod, the data can be presented when you have *very* few samples to work with.
>>>>> That said, it is interesting to watch it bring up error bars (which are indeed correctly calculated)
>>>>> and then see the trace walk outside those error bars as the run progresses.
>>>>> There are other measurements that are a bit less susceptible to this.
>>>>> None of them have any magic to get around sqrt(N).
>>>>> 
>>>>> Bob
>>>> 
>>>> Maybe I don't understand error bars. For a dynamic display like TimeLab, walking outside (1 sigma) error bars is expected about 1/3 of the time, no?
>>> 
>>> Error bars works a little differently, as they indicate with some probability (say 1-sigma) within which range the real value is.
>>> 
>>> By the way, sqrt(N) is not very accurate estimator.
>> 
>> But it is a common way to express the fact that your data is unlikely to converge any faster than sqrt(N)…
> 
> Yes, but it gives you false hope of how quickly it really converged, as the cross-correlations make you converge even slower than sqrt(N).

Except that management would really like it to converge as N …

Bob

> 
> Cheers,
> Magnus
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