From: Stan Hilliard shilliard@samplingplans.com
Date: 06 May 2003
Time: 23:29:03
Greetings Kevin,
Perhaps each update of that standard is worse than the one before.
I have a copy of Z1.9-1980. In it, the y-axis of the oc curves have the same size spaces between 50 to 60 as the other "decades".
In my copy of Z1.9-1980, the value in table B-5, at (1.69,10) is 3.52.
The Z1.9-1972 (prior to mine) was supposed to correspond directly to Mil-Std-414. One user of my software program TP414 complained that the program didn't agree with his Z1.9 oc curve. I checked out and confirmed that the program agreed exactly with Mil-Std-414, but not with Z1.9-1972.
I inquired to the ASQC standards committee for Z1.9 and was told that the making of the graphs was outsourced to the book publisher.
I think that this confirms that any process will move away from its target over time -- unless a mechanism is provided to detect that drift and adjust it back to target. That mechanism is called "quality control".