There are many applications where normal X-Bar Charts will not work. The X-Bar Chart as proposed by Walter Shewhart is based on within subgroup variation.

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Modified Control Charts are normally used for data with subgroup size greater than 1, say 5.

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Once a process is in control and variability well within specification limits, e.g. Cp>3, it maybe be reasonable to allow the process to drift a little within specification limits, without any noticeable effect, whilst appreciating that there is a cost in unnecessary tight control.

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Standard control charts consist of outer control limits and sometimes warning limits. Some analysts will enhance these charts with run and trend tests to increase the sensitivity to detecting variation due to assignable causes.

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U Charts are used to control the number of defects. Defects must not be confused with defectives. A defective part has one or more defects.

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SPC Charts were formally introduced over 100 hundred years ago by engineers and statisticians, such as Walter Shewhart, a self-taught statistician. These pioneers recognized and understood the concept of variability.

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Percent Charts are used for the same applications that P Charts are used i.e. to control the fraction of non-conforming products, although they can be used to also control fraction conforming (yield).

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P Charts are used to control the fraction of non-conforming products, although they can be used to also control fraction conforming (yield). Control limits are based on the binomial distribution.

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NP Charts are used for the same applications that P Charts are used i.e. to control the fraction of non-conforming products, although they can be used to also control fraction conforming (yield).

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Once a process is in control and variability well within specification limits, e.g. Cp>3, it maybe be reasonable to allow the process to drift a little within specification limits, without any noticeable effect, whilst appreciating that there is a cost in unnecessary tight control.

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A six sigma process that is centered at target has a Cp and Cpk index of 2.0. A six sigma process assumes that a shift in process average as high as 1.5 standard deviations from target will not cause perceivable problems.

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The EWMA chart has the same application that the moving average chart has. It is an alternative to the Shewhart X-Bar or Individuals chart when it is important to detect relatively small changes in the process mean.

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The Cusum chart is arguably the most sensitive classical control chart for detecting shifts in the process mean. Whereas a Shewhart X Bar chart can take a one standard error change a Cusum chart only takes 9 points on average.

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C Charts are used to control the number of defects. Defects must not be confused with defectives. A defective part has one or more defects.

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Because it is so easy to calculate and understand the range, over the standard deviation, the X-bar and Range chart is often preferred over the X-Bar and S control chart.

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Because it is so easy to calculate the range, the X-bar and Range chart is often preferred over the XBar and S control chart. However, it is recommended that the subgroup size is less than 10.

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The moving average chart is used as an alternative to the Shewhart X-Bar or Individuals chart when it is important to detect relatively small changes in the process mean.

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The Individuals Control Chart is used when rational subgrouping has little effect. One example is fast automatic filling lines.

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