[time-nuts] crystal againg fit (was: Excel logarithmic function)

Bob Camp kb8tq at n1k.org
Thu Nov 24 18:18:29 EST 2016


> On Nov 24, 2016, at 10:49 AM, Attila Kinali <attila at kinali.ch> wrote:
> On Thu, 24 Nov 2016 08:16:08 -0500
> Bob Camp <kb8tq at n1k.org> wrote:
>> If you take the bad aging (out of spec) parts out of the pile, those are the ones
>> with the best fit. They have very pretty curves and they stick to those curves
>> for a *long* time. They have a single dominant cause for their aging ( = the defect). 
>> The rest of the parts have all of the causes bashed down by the process so that
>> over a 20 or 30 year span, there probably is no single dominant cause. 
> Then the question becomes: What would be a good fitting function for
> the typical application of an OCXO that is regularly measured with
> not too long time spans (e.g. GPSDO)? From the discussion it seems
> that a second or third order Taylor would be sufficient to capture
> aging for a span of 10-100 days.

Simple answer no. More complex answer: what are you trying to do? Depending
on the answer to that there may be other functions that are useful. In general 
an unconstrained polynomial is great for fitting the data you have and awful 
for predicting the future. 


> 			Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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