Process Stability

Reliable analysis requires at least 20 subgroups to evaluate process stability and capability. Control limits determine stability. Once these limits are defined, the application evaluates each subgroup to confirm that the subgroup stays within the limits and does not violate trend tests. The application marks a subgroup as a violation when that subgroup fails a control‑limit check or a trend check. Subgroups are visually indicated with these color-coded symbols:

• Green square: In-control
• Yellow triangle: Out of control
• Red ellipse: At least one sample in the subgroup is out of specification (beyond the USL or LSL)

If no violations occur throughout the selected analysis period, the process is considered stable. The summary report, located in the bottom right corner of the chart, displays the total number of subgroups analyzed and the stability of the process. If the process is reported as unstable, only the subgroup with the latest violation is identified.