An overall capability index that measures whether the process meets specification and is on target. Cpm compares the specification spread to the spread of your data, taking into account the data's deviation from the target value instead of its deviation from the process mean. Large distances between the target and your observations result in a small Cpm value. As your process improves and approaches the target, the value of the Cpm index increases.
Compare your Cpm value to a benchmark value to determine whether to improve your process; many industries use a benchmark value of 1.33. If the values of your index are less than the benchmark value, you must take steps to improve your process.
The middle vertical line is the target value. The right and left vertical lines are the upper and lower specification limits.
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This process spread falls within the specification limits, but it is not on target. This process will have a poor Cpm value. |
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This process spread falls within specification limits but not on target. But it is closer to the target than the above graph, so its Cpm value is better. |
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This process spread is within the specification limits and on target. This process has the greatest Cpm value. |
If the process is exactly centered on target, the Ppk and Cpm values will be equal. Cpm is calculated only when you provide the target value.
