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Also, ISODAT uses the average of the two reference ratios that sandwich 
(before and after) the sample ratio




On 6/24/2011 8:22 AM, Gilles St-Jean wrote:
>
> Hi Corentin
>
> See answers below.
>
> Gilles
>
> > -----Message d'origine-----
>
> > De : Stable Isotope Geochemistry [mailto:[log in to unmask]] De 
> la part de
>
> > Corentin Reutenauer
>
> > Envoyé : 17 juin 2011 10:01
>
> > À : [log in to unmask]
>
> > Objet : Re: [ISOGEOCHEM] Delta value calculation
>
> >
>
> > Hi Jens,
>
> >
>
> > I have tried to duplicate isodat data as well (from dual inlet) and I am
>
> > very close to get the exact result (change in the 7th decimal place 
> of the
>
> > delta value). It is not possible to change the significant numbers 
> displayed
>
> > for the "intensities" (3) in the results (.did files), but if you look at
>
> > the plot below (on the same .did file), you can display a table with 6
>
> > decimal places for the signal.
>
> >
>
> > However, I'd very much like to know what precision Isodat is using for
>
> > intensities.
>
> Isodat uses all the digits available in the computer to calculate 
> everything.  What you see is for display only.
>
> >
>
> > What I wonder is whether the impossibility to duplicate Isodat 
> calculation
>
> > is due to a lack of infomation on intensities, or due to the fact 
> that there
>
> > are different steps involved from intensity to delta value, and 
> Isodat might
>
> > round those numbers during the process (eg. delta1 and delta2 which 
> are then
>
> > averaged to get the "true" delta value)
>
> Calculations of ratios are done on the areas not the intensities; 
> unless you are talking about dual-inlet.  If you want to see more 
> digits (up to 15) then go to the Configurator/ Options/ Global 
> Settings and adjust the digits you want to see under the "Value 
> Formats".  These settings will also export to Excel the full digits 
> you specify here.
>
> >
>
> > Best regards,
>
> >
>
> > Corentin
>


-- 
Greg Michalski
Assistant Professor
Department of Earth and Atmosperic Sciences
Purdue University
http://www.purdue.edu/eas/michalski/