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chadkjackson
User Rank
Iron
Re: One has to question the source
chadkjackson   3/18/2013 12:45:59 PM
NO RATINGS
TJ, saw your comment and wanted to respond.

As far as my background goes, you can see it here: http://www.lifecycleinsights.com/about-author/. I blog and write about the technologies that engineering organizations use to design and develop products. My company providers services for engineering organizations (http://www.lifecycleinsights.com/services-eng/) as well as technology providers (http://www.lifecycleinsights.com/services-soft/).

I blog at a number of places, including ENGINEERING.com (http://www.engineering.com/DesignSoftware/DesignSoftwareArticles/articleType/AuthorView/authorID/134769/Chad-Jackson.aspx), where I provide some frank insights on the direction of these types of technologies. I also blog at the new NAFEMs blog (http://www.nafems.org/blog/). I also co-host a webshow called Tech4PD (http://www.engineering.com/Videos/Tech4PDShow.aspx).

I've included this detail because you seem interested in what I do professionally.

I've written about a blog series on the engineering notebook and how calculations fit in (http://www.engineering.com/DesignSoftware/DesignSoftwareArticles/ArticleID/4682/Calculations-and-the-Engineering-Notebook.aspx). That led me down the path to write the eBook referenced in this post. I developed it independently. PTC licensed the publication and is hosting it on their web site for access.

As far as my site, lifecycleinsights.com, you'll find that none of my publications, presentations, web shows and whatnot are hosted there. By no means am I trying to start a media company like Design News. Instead, companies license my content and host it elsewhere like PTC or ENGINEERING.com for their own purposes.

I hope that answers some of your questions. Let me know if you have others.

Chad Jackson

 

BrusselsSprout
User Rank
Gold
Re: One has to question the source
BrusselsSprout   3/18/2013 10:39:25 AM
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I would question the source if I did not know it to be true.  However, if we limit the discussion to the primary spreadsheet program, MS-Excel, there are known documented issues with the functions built into Excel.  Random is not random, stdev is not the true standard deviation, linear regression is not least squares fit.....  The list of statistics errors in Excel is legion.  The frustrating thing is that MS has known about these errors and has not fixed them.  Even when they implement a fix in a new version it turns out to be broken in a new way. 

Microsoft has clearly abandoned a great market in Engineering and Science and only seems to care if money adds up correctly.  I suspect the monetary errors listed in the article were user generated.   The statistic function errors in Excel are built in.

Droid
User Rank
Platinum
At least you can see the formulas
Droid   3/18/2013 10:06:30 AM
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There is a skeptical side of most engineers that demands to verify everything and assume very little. Last time I checked - (unless the spreadsheet is locked) formulas are easily visible and we can see how values are being calculated.  I prefer that scenario over feeding values into a software "black box", shaking it a bit and then accepting the answer.

ab3a
User Rank
Platinum
Advice from my mentors
ab3a   3/18/2013 9:25:33 AM
NO RATINGS
Years ago, when slide rules were still found in desks and calculators roamed the earth, my mentors gave me this advice:

"If you find that you can't do your initial estimates with a basic scientific calculator, STOP. If you find yourself digging out your textbooks and writing equations, STOP. --You are probably about to make a huge mistake.

"Someone before you has probably seen this problem and has an acceptable plant equation or rule of thumb that you can use. If you reinvent that wheel, the chance that you will make a mistake is very high. You should use those text books to validate or invalidate an approach, not to create new ones, unless the old approaches are clearly inadequate somehow and you are really treading on new territory."

And in the years since, I have used those textbooks to create new approaches, but only in a handful of cases.

The point about spreadsheets is much the same: If someone has written and validated software, USE IT. The chances of making a mistake when modeling with a generic tool such as a spreadsheet or writing your own modeling software are VERY high.

As engineers we have an obligation to our employers, clients, and to the public to get the correct answers. If there is prior art that you can use to help you in this process, USE IT.

 

Jake Brodsky

TJ McDermott
User Rank
Blogger
One has to question the source
TJ McDermott   3/17/2013 2:36:44 PM
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The author of the blog references a book by Chad Jackson and thoughtfully provides a link to it.

According to https://twitter.com/ChadKJackson, Mr. Jackson is the president and principal analyst of Lifecycle Insights.

Lifecycle Interests refers to the same e-book at this link: http://www.lifecycleinsights.com/solving-engineerings-calculation-compromise-ebook/

However, Lifecycle Interests does not seem to host the e-book on its own website.  The book instead is hosted at the web site of this blog's author, PTC.  The author's company does not host its own work?

One has to question the source for the conclusions of the blog (and by inference the book as well).

I don't necessarily disagree that spreadsheets can cause errors to propagate because they tend to hide the equations.  It does not negate their incredible usefulness.  Other commenters have already noted the need for testing and checking.  ANY tool needs that.  The software being pushed by the blog author needs it just as much.  It may make the process simpler, and add some helping hand, but it also needs to be checked.

 

TJ McDermott
User Rank
Blogger
Re: 91% error rate
TJ McDermott   3/17/2013 2:22:50 PM
NO RATINGS
Charles, one could as easily say 91% of hammer-driven nails are bent.  The thrust of that statement would be powder-gun or electric-gun driven nails go in straight.

91% of nails may be bent by hammer-wielders, but that doesn't mean they don't hold just as well as the gun driven ones.

 

Pubudu
User Rank
Platinum
Re: 91% error rate
Pubudu   3/16/2013 2:57:38 AM
NO RATINGS
Charles normally we always depend on the spreadsheets, If it is contain 91% errors what will be the best option to overcome this issue. 

Charles Murray
User Rank
Blogger
91% error rate
Charles Murray   3/15/2013 5:54:01 PM
NO RATINGS
Ninety-one percent of spreadsheets contain errors? The nice thing about handheld calculators (and sliderules before that) was that the engineer was more connected to the calculation. There's a subtle disconnect when doing the calculation in software on a spreadsheet, which makes it easier for a resulting number to gain a couple of zeroes and still not be noticed.

Pubudu
User Rank
Platinum
Re: Test Data
Pubudu   3/15/2013 2:05:05 PM
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Tekochip yes I also with you but my problem is when we changed the data sometimes sum functions has changed without knowing me. Is there a any method of locking the formulas after checking the test data. 

Pubudu
User Rank
Platinum
Re: Test Data
Pubudu   3/15/2013 2:00:44 PM
NO RATINGS
Thank you very much for the very informative article, actually I have some bad experience with spreadsheets, But my mind did not like to believe that it is with the spreadsheets fault always in my side. Now I know what has gone wrong. 

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