Control Chart Chooser 🎉 📈

Answer 2–3 questions → get the right chart (p, c, or X̄–R)

1) What type of data do you have?

Measurements with units (grams, seconds, mm) are continuous. Pass/fail or counts are attribute.

Advanced notes (optional)

Constant sample size & defective units → np‑chart (variant of p‑chart).
Variable opportunity/time/area & defects → u‑chart (variant of c‑chart).
Large subgroups (n ≥ 10) → X̄–s is common; we focus on X̄–R here.

Quick Reference ✍️

p‑chart — percent defective

Use for: wrong items, late orders, seal leaks

p̄ = total defectives / (n × k)
UCL/LCL = p̄ ± 3 √[ p̄(1−p̄) / n ]

c‑chart — count of defects

Use for: scratches per panel, broken chips per bag

c̄ = average defects per unit
UCL/LCL = c̄ ± 3 √(c̄)   (LCL ≥ 0)

X̄–R — measurements

Use for: weight (g), time (sec), length (mm)

UCL/LCL(X̄) = X̄ ± A₂ R̄
UCL/LCL(R)  = D₄ R̄,  D₃ R̄

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