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how to calculate sample size

Six Sigma – iSixSigma Forums Old Forums General how to calculate sample size

This topic contains 46 replies, has 10 voices, and was last updated by  Mike Carnell 14 years ago.

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  • #38943

    AT
    Participant

    Hi ! everyone. I am trying to do SPC in our company. I could not calculate the sample size. Could you please help me to solve my problem.
    We manaufacture part in Milling machine, we had a batch of 250parts and it will be done in 3/4days after working both shifts. Actually they produce 4-5 parts per hour. And even in one part worker has to measure 10-15 dimensions ..like length , width , diameters etc..we had lots of reject in dimensioning issue and tolerance is about +/- 0.001 inch. So, if my condfidence level is 95% how do I calculate the sample size and what will be my sub group size??  how do take the random sample? Do I have to consider only for one shift or for all shift for all days until job is done. What do I have to do if I have to perform same thing in different parts but lot size is too small like 50parts?
    I tried to calculate form https://www.isixsigma.com/offsite.asp?A=Fr&Url=http://www.surveyguy.com/SGcalc.htm
    but it ask for margin of error . What does that mean??
    Thanks
    Ramesh

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    #117298

    Darth
    Participant

    I think this is a good question for Jakel to respond to.  This will give him ample opportunity to show off and contribute for the first time.
    In the event he wishes to remain as a bystander offering only insults, here are some thoughts:
    Are you trying to gather samples to make inferences about some continuous variable like dimensions or just pass/fail?  The link to the sample size formula was for discrete data not continuous.  In fact, why are you sampling?  What information are you trying to collect?  Would a control chart be more useful to you?  You mention subgroup size and that you make 4-5 an hour.  In that case, sample size becomes less of an issue.
    Three things affect sample size; desired confidence (usually 95%), some estimate of the population variation (usually an estimate of s.d.) and desired precision (what your site called margin of error).  Population size is only an issue when it is small relative to the calculated sample size.
    This should get you started.  Can’t wait to see what Jakel has to offer to the discussion. 

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    #117301

    miranax
    Participant

    As you can deduct from Darth’s remarks, this forum is characterized by a never-ending race to out wit and ridiculize people who “don’t do their homework”.  Darth’s explanation is pretty much how you should start.  This will get interesting….

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    #117303

    Bart
    Participant

    Your answer is embedded in the statement that you produce 4-5 pieces per hour.  That alone suggests X, mR as your monitoring tool (i.e., why wait an hour to collect 5 pieces to be measured as though a single subgroup? — you would absolutely lose the aspect of real-time process monitoring/responsiveness).  You could even begin by measuring every produced piece, separately charting each of the 10-15 dimensions.  Then after collecting some history, cut back test frequency for those dimensions proven clearly capable and controlled, focusing testing resources on controlling the less capable dimensions most putting process success at risk.

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    #117304

    Dayton
    Member

    Jeeze…  where to begin…. and not wanting to “ridiculize” you or anyone else, but…. If you “deduct” from Darth’s answer you are removing something from it, making it less that it was at origin – which, considering his answer, from a purely physics and law of nature standpoint would be impossible … possibly you meant “deduce” which is making a determination from…. but I do agree that asking things of the forum that could/should have been self-answered by a little research is like leading with your chin in boxing or possibly your ear if boxing Mike Tyson…  Let’s hope you are prophetic and it gets interesting.
     Vinny

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    #117306

    AT
    Participant

    Thanks Darth,
    Yea, control chat is useful for me.I am trying do all these things to determine the process capability.I am  trying to gather samples to make inferences about some continuous variable like dimensions not a pass/fail.
    Please let me know how to start ?? and what would be sample size.
    Thanks
    Ramesh 

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    #117308

    miranax
    Participant

    my bad…
    In any case, Darth is pretty helpfull and straight forward with his answers.  I didn’t want to imply it was him who uses this forum to show the world how much he knows about Six Sigma and how little the rest-of-the-world does (to put it in mild terms).

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    #117310

    Dayton
    Member

    Yeah, I know.  He’s OK, but go light on the compliments, he already has a big head – at least a big black plastic alien helmet so I’m assuming he’s got a big head.
     Vinny

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    #117323

    Darth
    Participant

    Sorry that use of the Forum has been reserved by the Webmaster for the sole or soul use of Stan the Man.

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    #117337

    mand
    Member

    Bart: I second your motion as the more pragmatic of all those proposed.
    Regards.  Sam-

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    #117408

    Deep
    Participant

    I agree with Bart and Darthy- to explain it again….
    1) Startup with control charts (I,MR,R might be helpful for you since you are saying that you are getting lots of failures- part of reason might be a combination of variation of within and between subgroups)- Compare those charts with Xbar and R. Based on this, you can get an idea of where the variation is coming from)
    2) Since you are getting lots of scrap -you might expect OOCs in the charts, it is worth to identify the causes of variation rather than spending your energy on Capability indices
     

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    #117420

    Markert
    Participant

    Deep,
    Its been Dr. Darth, Mr. Darth, Dorth-ey, Shirley, Stan’s alter-ego Darth, Daddy Darth, Dad, DD, Dark Side Dude, Plastic-face-why-the-heck-does-he-wear-that-cape-in-here?, Darthette, Darthella, ‘man that guy was scarey, I’m glad he’s gone; who get’s his stapler?’ as well as others, but I don’t remember Darthy.
    Ok, we’ll make an exception. Welcome, Darthy!

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    #117423

    Darth
    Participant

    Phil, you have earned the right to address me in the familiar but I don’t believe Mr. Deep has. 

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    #117430

    Markert
    Participant

    Darth:
    Let it hereupon be know that with the power invested in me as Co-Master of Ceremonies of the oftmentioned Six Sigma Carnival and Dead Mathematicans and Statisticians Theme Park and Chief-Non-value-added Thread Starter, also known as COMAC-NADS, I propose a body of like minded individuals consolidate our efforts and spin-off from the traditional area of Six Sigma into the newly formed Sxxt Sigma, using anything we can boost from the existing body of knowledge and giving full credit to naming such a body to our esteemed Darthy. We will steal from everyone except TxTx, who apparently has already got lifting of others work covered and who has had some difficulty supplying much needed Vegematic julian french fry/branch chippers and copywrite violation machines for the forum spring program. 
    We shall ask Vinny to be chairman of the Board of Standardization, (BS) to see that the errors of the past are not repeated and that all credential standardization activities are handled with Common Sense. He can also issue standardized animal crainial adornment instructions. 
    20 years from now, I can see it now. People all over the world visiting a here-to-only-imaged Internet forum and asking the question, “But why Sxxt Sigma, and please tell me about that 1.5 sigma shift?”
    Who’s with me?  

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    #117432

    Dayton
    Member

    I’m with you!!!!!     Six Sigma’s New Frontier and Next Generation.
     
    Although you have a grand idea with COMAC-NADS you lack an integrated approach that could be achieved if you had a Governance Office which established the overview rules of the road much like that of a new ISO process with the more granular descriptors and processes found in the BS papers and procedures of the Board of Specialization.   The integration that you are lacking, i.e., Governance Office and COMAC-NADS, would give you the GO-NADS required to really make this work. 
     
    But, nonetheless, even with a great deal of quasi-administrative structure to develop and, frankly, tons of BS paper yet to be conceptualized and issued from my office in the Board of Standardization – I’m in!!!
     
    Yours in fond support of advancing the concept and profitable deployment of Sxxt Sigma and eternalizing the 1.5 Sigma Shift Stigma. 
     Vinny

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    #117436

    Darth
    Participant

    By Golly, I believe we have hit upon the final solution to those incessant posters wanting us to do their homework assignments for them, for example the recent nonsense about Poisson.  I guess there are other important roles to be filled such as:
    VP of Libation Procurement – possibly Carnell
    VP of Diplomatic Relations – possibly Stan
    VP of Publications – I got this one.  isixsigma magazine will not be able to compete with what I have in mind.  The first issue of Sxxt Sigma will have a centerfold of you know who….and it ain’t B of A.  The second issue will feature the yodling girl from Sweden that Rubber Guy had the hots for.  By the way, whatever happened to him????  Milton Jones will write an article on how to spell DMAIC.  Each issue will feature a dead Italian Math guy or possibly one soon to be dead.  Reigle has agreed to host the Ask Mikel column in which all his replies will consist of how great Dr. Harry is and that he didn’t really steal SS from those more worthy.   Bill Smith’s fake grand daughter will provide recipes for snacks to be served at Team meetings.  Dog Sxxt will rant and rave on the back page about something no one will be able to understand or read.  I can go on and on with ideas. 
    I believe I have solved the financing issue as well.  Carnell has graciously agreed to donate a portion of his earnings from his collection of published masterpieces on SS.  That should more than cover the nut of GO-NADS.
    There are still many more positions to be filled with the many great contributors we will steal from isixsigma.  Thoughts anyone?  Volunteers? 
    Sincerely Shirley

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    #117438

    Markert
    Participant

    Darth and Vinny:
    Your enthusiastic support is overwhelming. I have never felt so happy that we may be able to blaze this trail together. I am overwhelmed and nearly speechless. Well, maybe not.
    Process improvement and adult entertainment, my two favorite topics to read about. (I generally like to look at the pictures in my process improvement periodicals.) Can’t wait for the first issue.
    I believe that with Vinny skillfully utilizing all of his Common Sense in GO-BS, and selecting the necessary certification skills and content we will be on our way to a high performing branch dogma, one which Dog Sxxt may even approve of though likely no one could tell whether this is so. But, and there is always that but….
    What to do about the 1.5 sigma shift? I propose that the only statistically applicable method of assuring that the vast majority of the incessant posters needing to be spoonfed is to teach a 6.0 sigma shift as part of our Sxxt Sigma off-shoot. I say by making it easy to do, and easy to understand, and easy to embellish on success stories, we’ll have the books, consulting gigs, and commercial TV exposure on shows like Oprah, and others available for our message. We need to get ahead of the curve and get into the mass market.
    Darth, excellent ideas on the content of the new magazine. And I’ll bet there is someone right this minute writing a case study about our successes in Arabic as we speak for a future issue. But, I had another role in mind for you….
    Every movement needs a face man. Not to be confused with periodic poster here, Faceman. In your case you’ll be our Mask Man.
    Who will lead this new movement; this new movement that we are starting, to an eventual role of “the movement I started” maybe 15-years down the road? Who will it be who emerges as the founder and chief check casher for the work of so, so, so many involved in this effort?
    Who has the courage, the skill, the ego and GO-NADS to emerge from the pack to lead this charge? Who has the pointy elbows and sharp words to make things happen in this forum? Who? I think you.
    But only if the infrequent, lone female, who happens upon our nearly exclusively male forum gets to see you in a swimsuit and approve. Why are there so many men here and so few females anyhow? Please e-mail pics to MC so he can have his IT guys install a tab/button under “New to Six Sigma” for “Sxxt Sigma’s New Leader” so the that lone girl can vote on your pic.
    Any other thoughts? Come on, we’re doing something big here!

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    #117439

    Mikel
    Member

    VP of Diplomatic Relations – possibly Stan
    I accept – “Shoot the stragglers and carry the wounded”

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    #117440

    Markert
    Participant

    “So, the stragglers will be forced to do shooters and the wounded will carry them to them.” That’s all you can come up with? Stan, were doing something great here! Pitch in!

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    #117441

    Darth
    Participant

    Phil, I am sure that they taught this at a Home Depot workshop but how do I insert a picture in a post?  The traditional copy/paste doesn’t seem to work.  I am flattered that you want me to lead my…I mean our movement.  I would be happy to post a pic in a Speedo for the lone female or for someone who will soon be.  Just let me know how.  Thanks
     

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    #117443

    Markert
    Participant

    Darth, a bit off the mark in what I wrote, but I’ll run with it anyway….
    I think they may have covered that posting info during the day in the workshop the guys and I were practicing our jousting skills like King Arthur’s Knights using 2×2’s in the storm door area. Or maybe it was during the clinic on 101 ways to remove spraypaint. Or how to chase down wind blown carts in the parking area before a collision with a olde Vette. I just don’t remember. Sorry. Onward Sxxt Sigma!!

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    #117444

    Mike Carnell
    Participant

    Shirley,
    I will accept that position. On my next return I will procure the infamous Straw Rum of South Africa. We will participate in the local custom of holding a shot in your mouth as long as you can (before you swallow it – no spitting it out). You then spend the next day peeling the skin off the inside of your mouth.
    The expense of being multi-cultural.
    Regards

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    #117445

    Mike Carnell
    Participant

    Phil,
    There may be more truth to at least one part of your post than you may think.
    Regards

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    #117456

    Deep
    Participant

    thanks

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    #117467

    Markert
    Participant

    Mike,
    Thanks for that opportunity to set the record straight. As a forum elder, and one of the few members to have an actual photo on file at isixsigma cyperheadquarters, you are as usual, correct. And the photo neither involves some kind of springtime clean-up or wearing a Speedo.
    There was one part of the sequence I was not completely truthful about.
    There likely are two guys writing case studies in Arabic about our Sxxt Sigma efforts, even as we speak.

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    #117468

    Darth
    Participant

    If someone can provide some help, I can post a pic of Darth in a bikini. It might even surpass B of a S as the requested center fold for the first issue of iSxxtSigma magazine.

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    #117469

    Dayton
    Member

    Glad to help.
    Vinny

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    #117470

    Darth
    Participant

    Ok Man of Rigorous Program, how’d you do that?  In fact, I went out looking for one today but they are hard to find.  Guess I will order one online.  My pic is of the real Darth in a bikini but that might be too risque for this Forum.  How about I email it to you and you try posting it?

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    #117471

    Dayton
    Member

    Oh, Marginal One,
    Sure.  Get me booted off the forum AGAIN!!  
    How about you find a picture you want, right click and hold your mouse and drag the little arrow over the pictire (high lighting it), and then depress Ctrl and C at the same time, and then put your little arrow in the response section of a message posting and depress Ctrl and V at the same time.    The “C” key is for “Cool” and the “V” key is for “Vinny”.
    Vinny

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    #117472

    Darth
    Participant

    Despite a less vigorous program, I do know the C and V command.  It copies fine but no paste.  Can do it into other programs but this box.  Any other brilliant ideas?
     

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    #117473

    Dayton
    Member

    Nope.  It’s fortunate for me that the easy way worked.   Have you tried another PC?    It’s possible that it’s all in the wrist.   
    Vinny

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    #117474

    Markert
    Participant

    I wasn’t aware that posting personal photo’s from our collections were permitted. But now since you guy’s mentioned it,
    This photo I took last fall when Darth made his formal entrance at the ISSSSSSP convention. Note that a couple of guys from our store staff, in the orange company colors, decided to make themselves available to assure that he didn’t break a hip or something during the landing.
    Renting a plane and “just dropping in”…you show-off!!!!

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    #117475

    Markert
    Participant

    Here’s a photo of Darth getting ready to entertain some of the Star Wars gang in his specially designed living room, in fact the whole house looks pretty much like this…makes it easy to maintain and a quick mop up on the always present Florida dust bunnies.

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    #117476

    Darth
    Participant

    You guys should not be pirating my personal photos!!! There must be some copyright thing you are violating. Stop teasing me and give me instructions how to do the same. None of the standard copy/paste, control cool/vinny techniques are working for me. Does the picture have to be in a certain format? Should I save it as a jpeg, tif, gif, metafile, bitmap, etc.?

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    #117477

    Dayton
    Member

    I don’t have these technical issues to deal with – my kids occasionally take mercy on me, sigh, roll their eyes and say, exasperatedly, “OK, move over…”  
     
    My daughter in elementary school suggests that you just calm down, think about your steps, assure that you have really copied your picture, and then paste it into the posting commentary section.  
     
    She thinks that you are just too anxious and messing something up.  I’d listen to her if I were you, she scores 99th percentile in her state ranking tests and is in a whole bunch of advanced math, science and language classes – but she’s not always too patient with the older generation, so don’t expect a lot of help.
     Vinny

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    #117481

    Mikel
    Member

    Vinny and Phil,
    Remember the basic rules of giving instructions to a Lean Six Sigma MBB, PhD, FoS – talk slowly and give very, very detailed instruction for when Darth explains this to his administrative staff who does his posting for him.

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    #117482

    Mikel
    Member

    picture of Darth before he started hanging out in a bikini with the “boys” at 13th and Ocean on South Beach.

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    #117483

    Markert
    Participant

    Those must be his posse of “boys” following Darth in the old photo.
    It’s likely not a real good idea for Darth to turn his back now on those guys from 13th and Ocean on South Beach wearing his bikini, or to bend over and readjust his Florida-style socks and sandals.

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    #117487

    Darth
    Participant

    You guys are having wayyyy to much fun with this…at my expense.  Just wait until the new movie comes out and you try to get tickets.  I have instructed the studio to post pics….if they can figure it out….and you will be stopped at the door.  So there!!!!

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    #117492

    Markert
    Participant

    “I don’t know about you,” said Darth. “But being a Six Sigma professional is hard work. Constantly on the go… airports.. hotels… and constantly whining Green Belts and champions. Sometimes you just need to relax and decompress.”
                   
    “It’s at these times that I just like to take off the mask that has been restricting my natural breathing and let go of the numerous high-pressure activities of the day. Have a bottle of fine Don Julio and just relax. Give in to some downtime and just smile.”
    “And maybe put on my bikini and do a couple of laps in the hotel pool. I have to dry off extra well because my skin is sensitive and I have a tendency to grow extra eyes and fungus.”
    “Note to self,” thought Darth as he finished checking out the postings on isixsigma.com and drifted off to sleep. “Avoid any consulting with TxTx because they manufacture that vegematic french fry slicer/dicer and branch chipper copywrite violation device, and it’s real scarey!”

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    #117493

    Darth
    Participant

    You are a hoot.  Your talent and humor are being wasted in the HD paint department.  You could be doing so much more than running that paint shaker thing which I just found out is also made by TxTx.

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    #117494

    Darth
    Participant

    Phil, don’t you just hate it when those guys from the J.O. Club try to get me in trouble:
    http://www.wftv.com/news/3785486/detail.html
     

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    #117495

    Darth
    Participant
    #117496

    Markert
    Participant

    Darth:
    Quite the criminal mind on that guy. By the way, wasn’t pizza one of your favorite turn-on foods when you were spotlighted in the centerfold of a special issue a couple of months ago?
    But wait a minute, who would have complete access to a Darth Vader costume, a jail issued stun-gun, a fast getaway car, and live in Florida?
    If MJones, Milton Jones, MC, Carnell, Adam Bowden, Luke Skywalker, Babe of a Sister, or any/or all of the Stan’s turn up dead, or stunned, the three of us are comin to get ya! (Me, Vinny and Dog Sxxt, if we can figure out his directions to his home to pick him up…………)
    You’ve got a great sense of humor and a lot of fun, as well as a highly productive member of our little community. Things wouldn’t be the same here without you; we can tell Stan still has the DT’s when you’re out consulting.
    You’re not bad for a: 1) Plastic spud with optional eyeglasses, mustache and adjustable ears. 2) A deadly degenerate, space killer. 3) A humble, hardworking, professional, aPhD who fancies himself as Shirley with a bikini. 4) Our new leader of a less than groundbreaking knock-off called Sxxt Sigma. 5) All of the above.
    You’re allright.
     

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    #117497

    Markert
    Participant

    Darth:
    That would be a teriffic additional item if this was the Star Wars Spring/Fall program catalog, but alas, said sprinkler has nothing to do with Six Sigma with the exception of an indirect link to your screen name. Nice birddogging anyhow!!!
    Let the Dark Side defend your lawn from the ravages of summer heat or cool you off on a hot day with this Darth Vader sprinkler! Standing 10″ tall, this great new Vader sprinkler spins around with water spraying action, wielding his lightsaber in a furious battle to save your lawn! Let Darth Vader be the center of your backyard universe today with this very cool garden accessory.
    Now, if someone can quickly come up with a 1O” tall Jack Welch, Bob Galvin, Stan or Mike Harry sprinkler, we may have something!!!Even more so if the water is sprinkled from a non-politically correct location from the human body.
    Even greater interest if it mutters while sprinkling utilizing advanced microelectronics, “That’s nonsense” or “Go read Ohno.” 
    Such a sprinkler would be a perfect complement to the 9′ CEO Chia Shrub…..Imagine the potential!!!

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    #117511

    Darth
    Participant

    According to Stan, he is already using such a product on his back 40 acres.  It is a Mikey Harry fertilizer spreader.  As it moves along, it spews specially formulated b.s. in an ever wider circle.  Unfortunately, according to Stan there are two bugs in the product.  First, it only works in the desert of AZ where the grass don’t grow and for some reason, it dispenses the product 1.5 feet further on the left.  Since it is produced in China, Stan has put Dog Sxxt on the case and he hopes to have the problems rectalfied shortly.

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    #117539

    Mike Carnell
    Participant

    Phil,
    I think we are all relatively safe. I think that is Darth bdriving the boat in that new Evinrude E-TEC commercial. That thong may have opened up a whole new career for him.

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