SPC study and process capability calculator

Move from raw inspection readings to a traceable stability and capability decision. Build rational subgroups, validate the study, inspect control signals and export the complete evidence without sending measurement data to a server.

Start study

SPC / STUDY WORKBENCH

Build the study. Prove the process.

Measurement data stays in this browser. Nothing is uploaded to AccuTouch.

Browser-localNo login required

◇Study statusReady for data

StabilityNot assessed

Cpk—

Ppk—

Readings0

NG count0

Study information

Define traceability, specification and sampling conditions before analysis.

Measurement data

Enter exact readings manually, paste a matrix, or import a local file.

Subgroup	Reading 1

25 subgroups × 5 readingsValues are stored at entered precision and calculated without display rounding.

Readings / subgroup

Drop CSV or XLSX here or choose a file · processed locally

Decimal separator Header row

Data validation

Engineering data is never silently corrected, discarded or rounded.

◇

Waiting for measurements

Enter or import data to run traceable validation checks.

SPC analysis

Chart selection is based on rational subgroup structure, then remains visible in the report.

Control-chart method

Recommended methodWaiting for data

Add measurements to assess subgroup structure.

Interactive report

◇Not assessed

Control limits Specification limits

Control chartRun analysis to render the chart.

Control-rule violations

Statistical assumptions & warnings

View subgroup calculations

Subgroup	n	Mean	Range	Sample s

Report & exports

Preserve source readings, calculation method, exclusions and conclusions with the study.

Discuss this study with AccuTouchReview measurement strategy, software and process integration.

Transparent calculations for engineering review

Within-process sigma is estimated from the selected control-chart method. Overall sigma uses a numerically stable sample-variance algorithm. Capability uses the unrounded readings, while display decimals affect only presentation. One-sided specifications report only the applicable upper or lower capability index.

Control limits are calculated process limits. LSL and USL are design or customer requirements. Keeping them distinct prevents a common and consequential interpretation error.

Connect the study to the measurement system

AccuTouch SPC softwareMove from a browser study to configured production monitoring. Precision gaugesReview instrument resolution, fixtures and comparative gauging options. CNC AutoOffsetExplore bounded process-correction workflows after measurement validation.

SPC study questions

What is the difference between Cp and Cpk?

Cp compares the specification width with estimated within-process variation. Cpk also considers how far the process mean is from the nearest specification limit. Both require a suitable, stable study before formal approval.

What is the difference between Cpk and Ppk?

Cpk uses a within-subgroup estimate of sigma for short-term potential. Ppk uses the overall sample standard deviation and therefore includes longer-term movement present in the collected study.

Which subgroup size should I use?

Use rational subgroups that capture short-term variation under nearly identical process conditions. Individual observations use I–MR; fixed subgroups of 2–10 commonly use Xbar-R; larger fixed subgroups commonly use Xbar-S.

How many readings are needed for a capability study?

There is no universal count for every process. Smaller studies are shown as preliminary. Many procedures use at least 100 observations or 20–25 rational subgroups, but the approved customer or company method controls.

Can I approve capability when the process is unstable?

An unstable process has time-dependent behaviour, so a single capability estimate can be misleading. Investigate special causes, establish control and then assess capability under the approved procedure.