Six Sigma Quality API

Six Sigma and quality-engineering maths as an API, computed locally and deterministically — the process-capability and defect maths behind a quality programme. The capability endpoint takes a process mean, standard deviation and the upper and/or lower specification limits and returns Cp = (USL−LSL)/6σ and Cpk = min((USL−μ)/3σ, (μ−LSL)/3σ) together with Cpu, Cpl and the expected DPMO and yield from the normal tails — a centred Cpk of 1.33 is the classic capable-process target. The dpmo endpoint turns defects, units and opportunities (or a yield) into defects per million opportunities, the yield and the process sigma level using the conventional 1.5σ long-term shift — the famous six-sigma 3.4 DPMO, and 3000 DPMO landing at about 4.25 sigma. The yield endpoint rolls per-step yields into the rolled throughput yield Π(yieldᵢ) — the chance a unit passes every step defect-free — with the normalized yield and the total defects per unit, and can start from DPU instead. The normal tails come from an accurate erfc and the sigma level from an exact inverse-normal. Everything is computed locally and deterministically, so it is instant and private. Ideal for quality-engineering, manufacturing, Lean Six Sigma and process-improvement app developers, SPC and capability-study tools, and green/black-belt training. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 compute endpoints. This is the capability and DPMO maths; for general descriptive statistics use a statistics API.