Ryan Put Cpk into your search engine and you should get many references. I imagine the reason for this low Cpk was that the standard deviation was large even though the average was with in range. This indicates a poorly controlled process that has an unacceptable likelihood of producing unacceptable product, which is the purpose of the measurement. Best regards Lee J. Lee Parker, Ph.D. JLP Consultants LLC 804 779 3389 ----- Original Message ----- From: "Ryan Grant" <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, March 28, 2007 11:39 AM Subject: [TN] Explanation of Cpk (Ppk) Hi all, I have a supplier that is wondering why we rejected a shipment for finding a critical dimension as having a Cpk of 0.65 (Ok, technically, we are calculating Ppk). None of the 45 measurements were actually out of spec (although one measurement just missed exceeding the upper limit by 0.002mm). Now they want to know why we are rejecting for low Cpk. Sigh... Rather than go through the tedium of carefully explaining what a distribution is, what it means, how to calculate it and what the calculation implies, etc., does anyone know of some websites I can point them to that can explain this? Any help is appreciated. Thanks, Ryan Grant --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------