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View Full Version : Cp, Cpk, Sp, Spk for a one-sided minimum specification

bkearns
12th March 2004, 02:14 PM
Hey folks,

Can anyone out there tell me how to handle the calculations for a spec that is a minimum only? I want to analyze process data where the spec is >= 5 MPa there is no upper and lower spec limit.

Thanks in advance for any help you can offer.
bkearns
Atul Khandekar
12th March 2004, 02:33 PM
Welcome to the Cove, bkearns!

The issue has been discussed in the forums before, you'll find quite a few threads on Cp/Cpk issues if you do a forums search.

Just to get you started, check out the following threads:
Calculating Cpk on a single sided (unilateral) tolerance (http://www.elsmar.com/Forums/showthread.php?t=6552)
Cp and Cpk for Product with only LSL (Lower Specification Limit) (http://www.elsmar.com/Forums/showthread.php?t=6410)
Determining Cpk on a single sided tolerance dimension (http://www.elsmar.com/Forums/showthread.php?t=1882)
Narfeldt
16th March 2004, 07:03 PM
To calculate Cpk use the formula Cpk=(Average-LSL)/(3*sigma). Cp is N/A because you can't compare process variation against specification width.

What is Spk and Sp?