Free SPC Control Chart Generator

Paste your data, see control charts with Nelson rules and Cpk analysis instantly. Your data never leaves your browser — all calculations run locally.

Paste your measurement data

125 data points in 25 subgroups of 5 — chart type: X-bar R (recommended)

Chart type

Recommended: your data has 5 columns per row, matching subgroup size 5

Specification limits

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Pattern rulesNelson (8 rules)

X̄ UCL

25.0328

X̄ CL

25.0054

X̄ LCL

24.9779

R UCL

0.1006

R CL

0.0476

R LCL

0.0000

2 violations detected across 2 rules

Rule 5WarningSubgroups: 17, 18, 19

Two of three consecutive points beyond 2-sigma on the same side

Increased process variation near the control limits — may indicate an intermittent special cause such as loose fixturing, inconsistent material, or periodic environmental disturbance.

Rule 6WarningSubgroups: 15, 16, 17, 18, 19

Four of five consecutive points beyond 1-sigma on the same side

A process shift developing — the mean is drifting toward a control limit. Check for gradual changes in materials, settings, or environmental conditions.

Process Assessment

Unstable

Your process shows special cause variation. 2 pattern violations were detected across 25 subgroups. The process is not in statistical control — assignable causes should be identified and addressed. Enter specification limits to assess process capability.

Recommended Next Steps

Review subgroups 17, 18, 19 — two of three consecutive points beyond 2-sigma on the same side. Examine intermittent variation sources — loose fixturing, inconsistent material properties, or periodic environmental disturbances.
Review subgroups 15, 16, 17, 18, 19 — four of five consecutive points beyond 1-sigma on the same side. Process mean is shifting — check for gradual changes in material, equipment settings, or environmental conditions.
Address special cause variation to bring the process into statistical control before assessing capability.

This assessment is based on statistical analysis of the provided data. It does not replace domain expertise or process knowledge. Always verify findings with process owners before taking corrective action.

Data Distribution

Data does not follow a normal distributionA² = 1.451 (critical value = 0.787 at alpha = 0.05)

Data does not follow a normal distribution. Capability indices assume normality and may be unreliable. Consider investigating subgroups for outliers, check for process shifts using the control chart, or evaluate whether a data transformation (Box-Cox) may be appropriate.

Enter specification limits (USL / LSL) above to see capability indices (Cp, Cpk, Pp, Ppk).

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