Process Control
Last updated on May 21, 2026
Yield summarizes the outcome of a Run, while process control reaches inside the run to expose every Measurement and every limit at the phase level.
You get two views: Cpk and control charts. For phase-level failure counts and durations, see Failure Analysis.
Process Capability Index (Cpk)
Cpk measures how consistently a measurement stays inside its limits. It applies to numeric measurements with at least one limit, and TofuPilot recomputes it in real time as new runs land.
Formula
The Cpk formula uses the mean and standard deviation of the selected runs.
Cpk = min[(upper_limit - μ) / (3σ), (μ - lower_limit) / (3σ)]Here, μ is the mean across the selected runs and σ is the standard deviation.
Interpretation
You can read Cpk against the same thresholds the industry uses.
| Cpk | Meaning |
|---|---|
| > 1.33 | Well-centered and stable. |
| ≈ 1.00 | Marginal. A small drift will start producing failures. |
| < 1.00 | Not capable. The failure rate is unacceptable. |
Capability table
The Capability table lists every numeric measurement on every phase, sorted by Cpk. Sort ascending to surface the weakest ones first.
Click a row to see Cpk over time. The view shows daily Cpk values for the lower and upper limits separately.
Control charts
A control chart plots a single measurement over time alongside its limits, mean, and ±6σ band, so you can spot drift at a glance.
| Measurement type | Chart |
|---|---|
| Numeric | Values, lower and upper limits, mean, ±6σ band, histogram with a Gaussian overlay. |
| Boolean | Expected values in green. Unexpected values in pink. |
| String | Expected values in green. Unexpected values in pink. When no validators are set, every value renders in gray. |
For numeric measurements, if the Procedure changes limits over time, the chart reflects the history with day-by-day limit curves.
Filters
Every process control view shares the same filter bar.
- Date range: pick a preset or a custom window.
- Source: choose user runs from CLI or production runs from a Station.
- Batch, procedure version, part name, and revision: slice the data the same way you would on the yield view.
- Phase and measurement: drill into one of either to render a control chart or a Cpk trend.
How is this guide?
Yield Analytics
Learn how TofuPilot computes first-pass, second-pass, third-pass, and last-pass yield per unit per day from every run you upload.
Failure AnalysisPreview
Find the weak step in your test with TofuPilot Failure Analysis: rank phases by failure count and wall-clock duration, then drill into the measurements behind each failure.