Launch the V-Mask CUSUM Control Chart Platform

Launch the V-Mask CUSUM Control Chart platform by selecting Analyze > Quality And Process > Control Chart > CUSUM.

Figure 6.4 The CUSUM Control Chart Launch Window

Identifies the variables that you want to chart.

Note: The rows of the data table must be sorted in the order in which you want them to appear in the control chart. Even if there is a Sample Label variable specified, you still must sort the data accordingly.

Sample Label

Specify a variable whose values label the horizontal axis and can also identify unequal subgroup sizes. If no sample label variable is specified, the samples are identified by their subgroup sample number. See Sample Label in Shewhart Control Charts.

Identifies a column that creates a report consisting of separate analyses for each level of the variable.

Two Sided

Requests a two-sided CUSUM chart when selected. If it is not selected, a one-sided chart is used and no V-mask appears. If an H value is specified, a decision interval is displayed.

Data Units

Specifies that the cumulative sums be computed without standardizing the subgroup means or individual values. The vertical axis of the CUSUM chart is then scaled in the same units as the data.

Note: Data Units requires that the subgroup sample size be designated as constant.

K Sigma

Specifies control limits in terms of a multiple of the sample standard error. Enter the K Sigma value in the box that appears below H. Control limits are specified at k sample standard errors above and below the expected value, which appears as the shift.

H is the vertical distance h between the origin for the V-mask and the upper or lower arm of the V-mask for a two-sided chart (for an illustration, see Figure 6.6). For a one-sided chart, H is the decision interval. Choose H as a multiple of the standard error.

Specifies reference value k, where k is greater than zero.

Sample Grouped by Sample Label

Indicates the column that identifies each sample. See Sample Label in Shewhart Control Charts.

Sample Size Constant

Indicates that the sample subgroups are the same size. See Sample Label in Shewhart Control Charts.

Specify Stats

Enter the following process variable specifications in the Known Statistics for CUSUM Chart area:

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Target is the target mean (goal) for the process or population. The target mean must be scaled in the same units as the data.

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Delta specifies the absolute value of the smallest shift to be detected as a multiple of the process standard deviation or of the standard error. This depends on whether the shift is viewed as a shift in the population mean or as a shift in the sampling distribution of the subgroup mean, respectively. Delta is an alternative to the Shift option (described next). The relationship between Shift and Delta can be computed as follows:

where δ represents Delta, Δ represents the shift, σ represents the process standard deviation, and n is the (common) subgroup sample size.

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Shift is the minimum value that you want to detect on either side of the target mean. You enter the shift value in the same units as the data, and you interpret it as a shift in the mean of the sampling distribution of the subgroup mean. You can choose either Shift or Delta.

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Sigma specifies a known standard deviation, σ0, for the process standard deviation, σ. By default, the Control Chart platform estimates sigma from the data.

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Head Start specifies an initial value for the cumulative sum, S0, for a one-sided CUSUM chart (S0 is usually zero). Enter the Head Start value as a multiple of standard error.

Delete Stats

Deletes all statistics in the Known Statistics for CUSUM Chart area.

Get Limits

Uses previously established limits that exist in a JMP data table. See Saving and Retrieving Limits in Shewhart Control Charts.

Capability

Measures the conformance of a process to given specification limits. Once you click OK in the launch window, if you have not already defined these as a column property, you are prompted to enter specification limits and a target. See Capability Analysis in the Basic Analysis book.