Business Mathematics and Statistics · Ch 9 — Applied Statistics (Time Series, Index Numbers, Statistical Quality Control)
Tolerance Limits and Control Limits
10
Tolerance Limits and Control Limits
Students often confuse control limits with tolerance (or specification) limits, but the two answer completely different questions and come from completely different sources.
| Control Limits | Tolerance Limits | |
|---|---|---|
| What they measure | Whether the process itself is behaving consistently (chance causes only) | Whether an individual finished item is fit for use |
| Where they come from | Calculated from the process's own data (, , and factors like , , ) | Fixed externally by the design/engineering specification or the customer's requirement |
| What they are plotted on | Sample statistics (, ) | Individual measured items |
| Question answered | "Is the process stable and predictable?" | "Is this particular item acceptable?" |
Definition 25Tolerance (Specification) Limits
The maximum and minimum values of a product characteristic that are acceptable to the designer or customer, fixed independently of the process's …