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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:
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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/