A statement about the spread of a process relative
to the specified spread, independently of the position
of the mean value of the corresponding product characteristics,
is given by the **c****p**
**value**. In contrast, the **c****pk**
**value** permits the spread width and
the position of the mean value of a process relative
to the closest "critical" specification
limit to be described

The minimum requirement is that the value of cp or
cpk should be greater than one. This means that the
range x = ±3s must lie within the specification
limits.