From: Stan Hilliard
Date: 27 Aug 1999
Time: 13:33:01
Greetings Mark,
Once you have a specification that the process can meet (or a process that can meet the specifications) there is question (Q2).
(Q2) How can you verify with data that this particular 200K part order meets the specification?
When you verify a specific customer order with data, that is an acceptance sampling issue, not for SPC. Fortunately, you can use the same data for both acceptance and control purposes, as long as both criteria are met.
Important -- avoid the AQL based Mil-Standards and the equivalent Z1.x-standards. These will only bury the facts, not only from your customer, but also from yourself. Don't use them. Many people would set your customer's specification of 99.99% to be AQL, which is wrong.
The instructions published in the AQL based standards actually promote that error, which has led to widespread misunderstanding as to what protection those plans offer.
For a good tutorial on modern acceptance sampling, go to www.samplingplans.com/modern3.htm
This is my website which also has areas covering best practices, software, and a Q&A discussion forum on sampling.
Sincerely, Stan Hilliard, CQE,CRE,CQA,PE shilliard@samplingplans.com