PQ Systems - Quality eLine
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Multiple control limits:
A long shot, or just a
bad slice?

Quality Quiz: With a video!

Data in everyday life

Bytes and pieces

FYI: Current releases

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Quality Quiz:Professor Cleary
Another quiz from Professor Cleary

Congratulations: "A" is correct!

Justin is correct in his assessment that the system is accurate. He might want to look further, to assure that it is precise. A useful visual image that helps to explain both accuracy and precision is one found in what was once known simply as “The Ford Manual,” but is known officially as Statistical Process Control (SPC) Reference Manual. The diagram below is taken from this volume.

The figure indicates four different possible states, with the circles representing targets and the dots standing for shots that are fired at the target. The upper left target shows that the shots have missed the bull’s eye, and that they are spread out. This pattern is considered to be neither precise nor accurate. The upper right diagram shows shots that are closer together, but that have missed the bull’s eye. This one is precise but not accurate: that is, the shots fall into the same similar range, but have not hit the exact target.

In the lower left is a diagram that shows shots that are accurate—that is, they are around the bull’s eye—but not precise, since they are spread out. And finally, the lower right pattern indicates shots that are not only close together, but also have hit the bull’s eye. This pattern is both accurate and precise.

Quality Gamebox, developed by PQ Systems, has another graphic explanation of the concept of accurate and precise that you may find useful. (And it’s fun!)

>> Watch a more complete video explanation

Quality Gamebox

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