In This Topic
Pp
Notation
| Term | Description |
|---|---|
| USL | Upper specification limit |
| LSL | Lower specification limit |
| Toler | Multiplier of the sigma tolerance (Minitab uses 6 as the default value) |
 | Overall standard deviation |
Cpm
Cpm is available only when a target is specified. Minitab calculates Cpm based on known values of LSL, USL, and T.
| Known value | Cpm |
|---|---|
| LSL and USL only | * |
| LSL, USL, and T = m |
 |
| LSL, USL, and T ≠ m |
 |
| USL and T only |
 |
| LSL and T only |
 |
| Either LSL or USL only | * |
Notation
| Term | Description |
|---|---|
| * | Missing value |
| USL | Upper specification limit |
| LSL | Lower specification limit |
| m | Midpoint between USL and LSL |
| T | Target value |
| Xij | jth observation in the ith subgroup |
| ni | Number of observations in the ith subgroup |
| Toler | Multiplier of the sigma tolerance (Minitab uses 6 as the default value) |
Ppk
PPM Total for expected overall performance
The expected number of parts per million that are outside of the specification limits, based on the overall variation of the process, is
Notation
| Term | Description |
|---|---|
| PPM | Parts per million |
| LSL | Lower specification limit |
| USL | Upper specification limit |
| Φ (X) | Cumulative distribution function (CDF) of a standard normal distribution |
 | Average of the observations |
| s | Overall standard deviation |
Z.LSL Z.USL Z.Bench for overall capability
Benchmark Z statistics for overall capability are calculated by finding the Z value using the standard normal (0,1) distribution for the corresponding statistics.
where:
Notation
| Term | Description |
|---|---|
| LSL | Lower specification limit |
| USL | Upper specification limit |
| Φ (X) | Cumulative distribution function (CDF) of a standard normal distribution |
| Φ-1 (X) | Inverse CDF of a standard normal distribution |
 | Overall standard deviation |
