Nonconforming units
Nonconforming units describe the number of nonconforming units a process produces, expressed in parts per million.
The number of nonconforming units is an alternative to traditional Cp and Pp indices. They are easily understandable by end-users.
The number of nonconforming units is either:
- The actual number of nonconforming units in the sample.
- The expected number of nonconforming units, assuming a normally distributed process quality characteristic with the parameters specified by the process mean and sigma. The process sigma is either the short-term or long-term sigma estimate.
Various indices measure how the process is performing against the specification
limits:
| Index | Description |
|---|---|
| < LSL | The number of nonconforming units that are less than the lower specification limit. |
| > USL | Thr number of nonconforming units that are greater than the upper specification limit. |
| < SL > | The total number of nonconforming units that are outside the specification limits. |
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