[To...] Posted March 13, 2023 Share Posted March 13, 2023 Below are some results from a program that was run 6 times without moving part. If I equate these standard deviation values to a probe qualification, I understand a lower number means the deviations were less. How do you interpret what is an acceptable standard deviation? I hear some people say "It was within 3 standard deviations." I understand this phrase but is there a relationship to the standard deviations on the report?Std Dev.JPG Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/ Share on other sites More sharing options...
[Ma...] Posted March 13, 2023 Share Posted March 13, 2023 I'm not really sure what your specific question is Tom. If it is related to GR&R or Process Capability studies, these topics are very well defined in the AIAG MSA manual (Automotive Industry Action Group, Measurement Systems Analysis). I think it is up to version 4. You can probably find a pdf of it with a Google search. Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37044 Share on other sites More sharing options...
[Ri...] Posted March 13, 2023 Share Posted March 13, 2023 Standard deviation is a calculation of the "variability" of the data. Here is a website that breaks down the math for you. https://www.calculatorsoup.com/calculat ... ulator.php The term "± 3 standard deviations" would only apply in the context of a Cpk analysis. By itself, standard deviation does not care about the USL/LSL, but Cpk does. Six Sigma or ± 3 standard deviations refers to how many times the standard deviation can fit inside of the USL/LSL - this is typically shown with a histogram (a bell-curve is the most common shown one). Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37046 Share on other sites More sharing options...
[Ri...] Posted March 13, 2023 Share Posted March 13, 2023 And so to answer your last question, just looking at the standard deviation without context to the specification limits is meaningless. Because a 0.01mm standard deviation might be significant on a ±0.02mm tolerance, but not so much of a ±2mm tolerance. Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37048 Share on other sites More sharing options...
[To...] Posted March 13, 2023 Author Share Posted March 13, 2023 Please sign in to view this quote. I prefer the following website for this...lol https://www.mathsisfun.com/data/standard-deviation.html 1 Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37050 Share on other sites More sharing options...
[To...] Posted March 13, 2023 Author Share Posted March 13, 2023 Please sign in to view this quote. I guess the question was really "What does the standard deviation do for me other than give me a warm, fuzzy feeling when it's really low?" Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37052 Share on other sites More sharing options...
[Da...] Posted March 13, 2023 Share Posted March 13, 2023 So the results in the attachment, are they from different machines? Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37054 Share on other sites More sharing options...
[To...] Posted March 13, 2023 Author Share Posted March 13, 2023 Please sign in to view this quote. No. A min and max result on a surface profile. Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37056 Share on other sites More sharing options...
[Da...] Posted March 13, 2023 Share Posted March 13, 2023 Contura ? Xt gold? Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37058 Share on other sites More sharing options...
[To...] Posted March 13, 2023 Author Share Posted March 13, 2023 Please sign in to view this quote. Prismo Ultra VAST Gold Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37060 Share on other sites More sharing options...
[Ch...] Posted March 13, 2023 Share Posted March 13, 2023 Please sign in to view this quote. By itself, STD.DEV is basically just a warm and fuzzy feeling. I'm preaching to the choir here, but it is just used to calculate other statistics. It's units aren't squared so it makes it easy to think about. On here, your data is for sure statistically different. That is to say that your data is different by much more than 3 std.devs. On here and using the STD.Dev from the the red part, the green part is about 100 std.devs above red part Link to comment https://qualityforum.zeiss.com/topic/8384-standard-deviation/#findComment-37062 Share on other sites More sharing options...
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