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'Necessary & Sufficient' Cover the Safety Level

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jhankwitz
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Sufficient is Subjective
jhankwitz   5/7/2014 9:10:18 AM
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Great article.  "Necessary" is often fairly easy to calculate knowing what is needed, but that "Sufficient" number can vary all over the place depending on perspective.  I think personal experience is a variable that can have great impact on what is sufficient, so can lead to a lot of debate among peers.  How safe is safe? How much is too much?

naperlou
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Re: Sufficient is Subjective
naperlou   5/7/2014 3:47:22 PM
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That is a good point.  The sufficient condition is usually the bounding condition.  The necessary condition is that which is called out specifically in the specification.  Of course, this assumes the requirements are correct.

Debera Harward
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Silver
Re: Sufficient is Subjective
Debera Harward   5/8/2014 12:08:58 PM
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Necessary is basically the requirement, the need, the necessaty and sufficient is basically having provided as much as needed .

jhankwitz
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Re: Sufficient is Subjective
jhankwitz   5/8/2014 12:32:04 PM
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I agree.  What I'm saying is that "sufficient" (as much as needed) is very subjective and based on individual perspective and opinion.  My wife and I have very different views on how many diamonds are 'sufficient' for her wardrobe. One may be necessary or required to display her merital status, but we don't agree on the sufficient number.

Debera Harward
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Silver
Re: Sufficient is Subjective
Debera Harward   5/8/2014 12:37:48 PM
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@totally agreed sufficiency of anything varries from person to person and no two person are alike so there perceptions , desires and wants cant be same however there needs can be same.

bobjengr
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Platinum
NECESSARY AND SUFFICIENT
bobjengr   5/7/2014 6:06:26 PM
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This is an excellent post--excellent.  I had a professor who always stated, " the only thing less desirous than an undersign is an over design.  He was all about applying the proper safety factors to design problems and stressed that to all of his students.  You were automatically "dinged" if you did not state and apply safety factors and how those affected the assembly of components.  

I think we have just seen a remarkable violation of "necessary and sufficient" with programming and launch of the "Affordable Healthcare Act".  A disaster due to improper planning and bogus architecture.  Our country could definitely benefit from reading your post. 

Cabe Atwell
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Blogger
Re: NECESSARY AND SUFFICIENT
Cabe Atwell   5/7/2014 10:25:15 PM
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That is a perfect example bobjengr. I don't think there's a finer example of what 'necessary and efficient' is all about. 

Battar
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Consumer
Battar   5/8/2014 9:09:33 AM
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In consumer products and appliances, the laws state - 

"necessary" = MTBF must be 3 months greater than the warranty period

"sufficient" = MTBF must be 3 months greater than that of your competitors' product

"Safety" = whatever is the minimum requirement to pass TUV/GS/ETL/UL certification.

jhankwitz
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Platinum
Re: Consumer
jhankwitz   5/8/2014 12:49:07 PM
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From where did you get these "laws"? According to these statements, "sufficient" is not attainable except for one producer.

Nancy Golden
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Platinum
Value of Engineer's Experience
Nancy Golden   5/11/2014 3:21:05 PM
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"It's often the engineer's experience and judgment that plays a key role in setting the numerical value for the factor of safety."

Reminds me of the chief engineer on the Enterprise:

[the U.S.S. Enterprise is being sucked into a black hole, seconds away from doom]
Scotty: I'm giving her all she's got, Captain!
[the bridge ceiling begins to crack as the ship's drawn closer]
James T. Kirk: All she's got isn't good enough! What else ya got?
Scotty: Um... Okay, if we eject the core and detonate, the blast could be enough to push us away! I cannae promise anything, though!
[the viewing window starts to rupture]
James T. Kirk:  DO IT, DO IT, DO IT!

Probably not a scenario he would have used a computer model for...

While a work of fiction, it still speaks to the importance of factoring in an experienced engineer's judgment that may not necessarily agree with a computer model...and that "sufficient" can also depend on the situation.

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