Control charts for standards
Shewhart, the Nelson rules and the two-sided CUSUM: what each chart catches, what it misses, and how to read them together.
A standard (CRM) goes into every batch to answer one question: is the laboratory still reporting the right value? The Shewhart chart answers it one result at a time and catches large errors at once. The CUSUM answers it across the whole run and finds a small bias long before any single result fails. A QA/QC programme needs both.
Read
Try
- Shewhart and CUSUM workbook: paste in one standard’s results and see both charts, the eight Nelson rules and the CUSUM signals.
- Change-point analysis workbook: look back over a run of results and find where the laboratory shifted, and how sure you can be.
In QC Analytical Results
The app draws the same charts for every standard, element and laboratory in your data. How it calculates them:
- Shewhart (SQC) control lines
- Nelson 8 rules
- CUSUM
- EWMA, another chart for small shifts
- Z-Score
- Glossary