Re: Capability for a minimum specification
If Cpk is an indication of how well centered the process is between the specification limits (and it is) how can you determine a meaningful index number if there is no "between"?
Your answer is the standard one in these cases, and it's what is usually done, but that doesn't make it correct. The problem is that when customers demand a capability study and a minimum Cpk result, they almost never understand what they're asking for, and why on its best day Cpk is only marginally useful, and at worst (which is most of the time) it's completely useless.
Trying to explain this to a customer is usually an exercise in frustration, but it's best to try to explain it anyway before resorting to fiction writing.