This article is a real great tribute, and should be teached in engineering schools. I found the "original" chart really interesting : although measuring a percent of defects, the lower control value is not set to zero ! In the early twentieth century, the ppm were not a sensible goal. Finding a percentage of defective parts too low compared to the average would probably have revealed a defective measurement system.
This article is a real great tribute, and should be teached in engineering schools. I found the "original" chart really interesting : although measuring a percent of defects, the lower control value is not set to zero ! In the early twentieth century, the ppm were not a sensible goal. Finding a percentage of defective parts too low compared to the average would probably have revealed a defective measurement system.