Hi all.
I am trying to make sure that I am doing this the right way. I hope you guys will look through my calculations.
First, I have a list of 42 measurements. They are presented lower on the page. LSL = 4.070, USL = 4.090. Now, I want to calculate Ppk from the data. I take the mean and SD of the complete data (42):
Ppk_upper = (USLXbar)/(3*sd)
Ppk_upper = (4.0904.079476)/(3*0.002640095)
Ppk_upper = 1.32879
Ppk_lower = (XbarLSL)/(3*sd)
Ppk_lower = (4.0794764.070)/(3*0.002640095)
Ppk_lower = 1.19646
Ppk = 1.19646, as this is the lowest

Cpk_upper = (USLXbar)/(3*sigma)
Cpk_lower = (4.0904.079476)/(3*0.001224)
Cpk_upper = 2.86601
Cpk_lower = (XbarLSL)/(3*sigma)
Cpk_lower = (4.0794764.070)/(3*0.001224)
Cpk_lower = 2.58061
Cpk = 2.58061, as this is the lowest
For Cpk I group the values below in pairs of two  as this is the sample size. Then I take the mean of each pair, and then take the mean of the means.
I find sigma for Cpk by taking find the mean range by subtracting the measurements in a pair from each other then taking the mean of them.
Sigma = mean of ranges/D2
Sigma = 0.001380952/1.128
Sigma = 0.001224
4,078
4,079
4,076
4,076
4,081
4,079
4,082
4,084
4,08
4,08
4,081
4,084
4,077
4,079
4,078
4,08
4,079
4,079
4,077
4,078
4,08
4,081
4,078
4,078
4,077
4,078
4,078
4,077
4,082
4,08
4,075
4,08
4,081
4,08
4,083
4,082
4,087
4,085
4,077
4,074
4,079
4,079
I am trying to make sure that I am doing this the right way. I hope you guys will look through my calculations.
First, I have a list of 42 measurements. They are presented lower on the page. LSL = 4.070, USL = 4.090. Now, I want to calculate Ppk from the data. I take the mean and SD of the complete data (42):
Ppk_upper = (USLXbar)/(3*sd)
Ppk_upper = (4.0904.079476)/(3*0.002640095)
Ppk_upper = 1.32879
Ppk_lower = (XbarLSL)/(3*sd)
Ppk_lower = (4.0794764.070)/(3*0.002640095)
Ppk_lower = 1.19646
Ppk = 1.19646, as this is the lowest

Cpk_upper = (USLXbar)/(3*sigma)
Cpk_lower = (4.0904.079476)/(3*0.001224)
Cpk_upper = 2.86601
Cpk_lower = (XbarLSL)/(3*sigma)
Cpk_lower = (4.0794764.070)/(3*0.001224)
Cpk_lower = 2.58061
Cpk = 2.58061, as this is the lowest
For Cpk I group the values below in pairs of two  as this is the sample size. Then I take the mean of each pair, and then take the mean of the means.
I find sigma for Cpk by taking find the mean range by subtracting the measurements in a pair from each other then taking the mean of them.
Sigma = mean of ranges/D2
Sigma = 0.001380952/1.128
Sigma = 0.001224
4,078
4,079
4,076
4,076
4,081
4,079
4,082
4,084
4,08
4,08
4,081
4,084
4,077
4,079
4,078
4,08
4,079
4,079
4,077
4,078
4,08
4,081
4,078
4,078
4,077
4,078
4,078
4,077
4,082
4,08
4,075
4,08
4,081
4,08
4,083
4,082
4,087
4,085
4,077
4,074
4,079
4,079
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