You're correct in that I should have provided more information.
The link below is a sample sheet with some nitrogen values, and more importantly, the equation(s) used. The agreement in values is more than adequate with these examples. Regrettably, I didn't make notes of the random values I used in testing that generated the least consistency.
Excel sheet: http://www.uark.edu/ua/isotope/book1.xls
php source in text format: http://www.uark.edu/ua/isotope/text.txt
I hope I didn't stir too much up in my inquiry.
Cheers,
-Tom
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
University of Arkansas Stable Isotope Laboratory
http://www.uark.edu/ua/isotope/
----- Original Message -----
From: Grzegorz Adamiec <[log in to unmask]>
Date: Tuesday, March 6, 2007 11:15 am
Subject: [ISOGEOCHEM] Microsoft Excel precision
To: [log in to unmask]
>
>
> I think it is a bit risky to state that Excel gives wrong results.
> We do not
> know which version of Excel is being used by the original post
> author. I
> think we should be presented with the mathematical formula, the
> formula in
> the Excel cell and the exact numerical values in which the
> difference has
> been observed. The difference may be due to rounding errors, the
> order in
> which the calculations are made etc. Floating point operations are
> approximate and TI-30 is very old (at least 25 years) so it may be
> due to
> the algorithms used there.
>
> If the way calculations in both cases are done correctly and in
> identicalway it is wotrth considering whether the differences are
> significant in
> comparison to the statistical uncertainty. It may turn out that after
> taking the uncertainty into account (its two significant digits), the
> difference is insignificant.
>
> --
> Dr. Grzegorz Adamiec
>
> Silesian University of Technology, Institute of Physics Department of
> Radioisotopes, GADAM Centre of Excellence Krzywoustego 2, 44-100
> Gliwice,POLAND tel. +48 32 237 2696, fax. +48 32 237 2254
> http://www.carbon14.pl/
>
> ------------------------------
>
>
> Hello Tom,
>
> The statisticians in my unit routinely warn us about Excel
> calculations, and
> this goes beyond statistics even to graphics. They cite several
> articlesshowing that Excel has problems, among which are:
>
> (1)
> <http://www.stat.uni-
> muenchen.de/%7Eknuesel/elv/excelxp.pdf>http://www.stat.uni-
> muenchen.de/~knuesel/elv/excelxp.pdf
> (2) D. McCullough B.; Wilson B. On the accuracy of statistical
> proceduresin Microsoft Excel 2000 and Excel XP.
> <http://www.ingentaconnect.com/content/els/01679473;jsessionid=3nn4j0onoc271
> .victoria>Computational
> Statistics and Data Analysis, Volume 40, Number 4, 28 October 2002,
> pp.
> 713-721(9).
>
> (3)
> <http://gcrc.ucsd.edu/biostatistics/Excel.pdf>http://gcrc.ucsd.edu/biostatis
> tics/Excel.pdf
>
>
> This being said, I use Excel all the time for calculations and for
> graphs,and suppose I will eventually be sorry.
>
> Tom Brenna
>
>
> At 10:56 AM 3/3/2007, you wrote:
> >Hello All,
> >We've been asked recently to provide results for a project in atom
> >percent instead of the usual delta per mil notation. It took a
> little
> >while to find the equations for this, so I decided to add one more
> >place online where this could be done. What I found in the process
> is
> >that if I convert delta per mil to atom percent using Excel, I get
> one
> >result. If I use my old TI-30, I get a slightly different result.
> If I
> >use php
> >(http://localhost/uasil/black/isotopes/delta_to_atom_percent.php),
> I
> >get the same result as with the TI-30. The results of the
> calculator
> >and php are different from what I get with Excel starting with the
> 3rd
> >to 5th decimal place, depending on the standard and isotope used.
> This
> >degree of precision is normally adequate, but I'd expect better;
> >particularly if I'm making a number of calculations. I'm assuming
> all
> >three tools have adequate floating point precision to produce similar
> results for more than just a couple of decimal places.
> >Why would there be differences after the 2nd decimal place with
> only a
> >few calculations (in the case of delta per mil to atom percent)?
> I'm a
> >little curious (concerned) as we use Excel daily for much more
> >complicated calculations.
> >Thanks,
> >-Tom
> >
> >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >University of Arkansas Stable Isotope Laboratory
> >http://www.uark.edu/ua/isotope/
>
> --=====================_1347542468==.ALT
> Content-Type: text/html; charset="iso-8859-1"
> Content-Transfer-Encoding: quoted-printable
>
> <html>
> <body>
> Hello Tom,<br><br>
> The statisticians in my unit routinely warn us about Excel
> calculations, and
> this goes beyond statistics even to graphics. They cite several
> articles showing that Excel has problems, among which are:<br><br>
> (1)<br>http://www.stat.uni-muenchen.de/%7Eknuesel/elv/excelxp.pdf">
> http://www.stat.uni-muenchen.de/~knuesel/elv/excelxp.pdf<br><br>
> (2) <font size=3D2>D. McCullough B.; Wilson B. On the accuracy
> of statistical procedures in Microsoft Excel 2000 and Excel XP.
> <a
> href=3D"http://www.ingentaconnect.com/content/els/01679473;jsessionid=3D3=
> nn4j0onoc271.victoria">
> Computational Statistics and Data Analysis, Volume 40, Number 4, 28
> October 2002, pp. 713-721(9). <br><br> (3)<br> </font><a
> href=3D"http://gcrc.ucsd.edu/biostatistics/Excel.pdf">
> http://gcrc.ucsd.edu/biostatistics/Excel.pdf <br><br> This being
> said, I
> use Excel all the time for calculations and for graphs, and suppose
> I will
> eventually be sorry.<br><br> Tom Brenna<br><br> <br> At 10:56 AM
> 3/3/2007,you wrote:<br> <blockquote type=3Dcite class=3Dcite
> cite=3D"">Hello All,<br>
> We've been asked recently to provide results for a project in atom
> percentinstead of the usual delta per mil notation. It took a
> little while to find
> the equations for this, so I decided to add one more place online
> where this
> could be done. What I found in the process is that if I convert
> delta per
> mil to atom percent using Excel, I get one result. If I use my old
> TI-30, I
> get a slightly different result. If I use php (<a
> href=3D"http://localhost/uasil/black/isotopes/delta_to_atom_percent.php"=
> eudora=3D"autourl">
> http://localhost/uasil/black/isotopes/delta_to_atom_percent.php), I
> getthe same result as with the TI-30. The results of the calculator
> and php are
> different from what I get with Excel starting with the 3rd to 5th
> decimalplace, depending on the standard and isotope used. This
> degree of precision
> is normally adequate, but I'd expect better; particularly if I'm
> making a
> number of calculations. I'm assuming all three tools have adequate
> floatingpoint precision to produce similar results for more than
> just a couple of
> decimal places. <br> Why would there be differences after the 2nd
> decimalplace with only a few calculations (in the case of delta per
> mil to atom
> percent)? I'm a little curious (concerned) as we use Excel daily
> for much
> more complicated calculations.<br> Thanks,<br> -Tom<br><br>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br>
> University of Arkansas Stable Isotope Laboratory<br> <a
> href=3D"http://www.uark.edu/ua/isotope/" eudora=3D"autourl">
> http://www.uark.edu/ua/isotope/ </blockquote></body> </html>
>
> --=====================_1347542468==.ALT--
>
> ------------------------------
>
> Date: Tue, 6 Mar 2007 12:54:11 +1200
> From: Peter Franz <[log in to unmask]>
> Subject: Re: Microsoft Excel precision
>
> I too once encountered a precision problem - it's been a while, but
> I think
> it was either in the exp() or log() function. I pretty much nailed
> it down
> to that - when I put my snippet of code into a Pascal file it
> worked without
> fault, but in Excel/Visual Basic it just produced crap.
>
> Peter
>
>
> On Tuesday 06 March 2007 10:26, Tom Brenna wrote:
> > Hello Tom,
> >
> > The statisticians in my unit routinely warn us about Excel
> > calculations, and this goes beyond statistics even to graphics.
> They
> > cite several articles showing that Excel has problems, among
> which are:
> >
> > (1)
> >
> ><http://www.stat.uni-
> muenchen.de/%7Eknuesel/elv/excelxp.pdf>http://www.>stat .uni-
> muenchen.de/~knuesel/elv/excelxp.pdf>
> > (2) D. McCullough B.; Wilson B. On the accuracy of statistical
> >procedures in Microsoft Excel 2000 and Excel XP.
> >
> ><http://www.ingentaconnect.com/content/els/01679473;jsessionid=3nn4j0on
> >oc27 1.victoria>Computational Statistics and Data Analysis, Volume
> 40,
> >Number 4,
> > 28 October 2002, pp. 713-721(9).
> >
> > (3)
> >
> ><http://gcrc.ucsd.edu/biostatistics/Excel.pdf>http://gcrc.ucsd.edu/bios
> >tati
> >stics/Excel.pdf
> >
> >
> > This being said, I use Excel all the time for calculations and
> for
> > graphs, and suppose I will eventually be sorry.
> >
> > Tom Brenna
> >
> > At 10:56 AM 3/3/2007, you wrote:
> > >Hello All,
> > >We've been asked recently to provide results for a project in
> atom
> > >percent instead of the usual delta per mil notation. It took a
> little
> > >while to find the equations for this, so I decided to add one
> more
> > >place online where this could be done. What I found in the
> process is
> > >that if I convert delta per mil to atom percent using Excel, I
> get
> > >one result. If I use my old TI-30, I get a slightly different
> result.
> > >If I use php
> >
> >(http://localhost/uasil/black/isotopes/delta_to_atom_percent.php), I
> > >get the same result as with the TI-30. The results of the
> calculator
> > >and php are different from what I get with Excel starting with
> the
> > >3rd to 5th decimal place, depending on the standard and isotope
> used.
> > >This degree of precision is normally adequate, but I'd expect
> better;
> > >particularly if I'm making a number of calculations. I'm
> assuming all
> > >three tools have adequate floating point precision to produce
> similarresults for more than just a couple of decimal places.
> > >Why would there be differences after the 2nd decimal place with
> only
> > >a few calculations (in the case of delta per mil to atom
> percent)?
> > >I'm a little curious (concerned) as we use Excel daily for much
> more
> > >complicated calculations.
> > >Thanks,
> > >-Tom
> > >
> > >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >University of Arkansas Stable Isotope Laboratory
> > >http://www.uark.edu/ua/isotope/
>
> --
> ============================================================
> Dr Peter Franz
>
> National Institute for Water and Atmospheric Research (NIWA)
> 301 Evans Bay Pde
> Private Bag 14901
> Kilbirnie
> Wellington
> New Zealand
>
> Ph : ++64-(0)4-386-0506
> Fax: ++64-(0)4-386-2153
> Mobile: ++64-(0)211-109304
>
> Email: [log in to unmask]
> Website: www.niwa.co.nz
> ============================================================
>
> ------------------------------
>
> Date: Mon, 5 Mar 2007 16:48:28 -0800
> From: Sam Ghidan <[log in to unmask]>
> Subject: Working with Zn Natural fractionation
>
> --0-1656316628-1173142108=:10981
> Content-Type: text/plain; charset=iso-8859-1
> Content-Transfer-Encoding: 8bit
>
>
> Dear Colleagues.
> if any one works to detect variations in the isotopic composition
> of Zn
> using the Double spike technique, then please just let us have more
> discussion about it.
>
> Variation in the isotopic composition of Zn is too small(<1 per
> mil) and
> it is too difficult to detect due to interferences accompanied with
> themeasurements. the main interference is the interference in the
> 67 isotope of
> Zn.
> Thanks
> Sam Ghidan
>
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