Different Cpk value which is calculated formula on the excel from the one calculated on JMP?

[#1]

Why Cpk value which is calculated formula on the excel is so different the one calculated on JMP?

[#2]

How does your Excel calculate Cpk? For JMP you can find the formula from https://www.jmp.com/support/help/en/18.0/#page/jmp/statistical-details-for-capability-analysis.shtml

[#3]

I found the problem. There was no lower limit but I did not put 0 for lower limit in JMP so it was so different. Now when I put 0 for lower control limit, it worked. Even there is no lower control limit, should I put 0 for this in JMP?

[#4 · Accepted solution]

If either of the specification limits is missing, the capability indices containing the missing specification limit are reported as missing.

If the limits are missing, I wouldn't put them there. Of course it depends a bit what you wish to see: do you just want to have same result as your Excel (again how your excel calculates Cpk and does it force you to have both limits and if it does, why?)? And in that case you might have to add 0 there (even if it could be incorrect).

[#5]

If there is no lower spec limit your Cpk = Cpu