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SPC & process capability

Statistical process control and capability: Cp, Cpk, Pp and Ppk (also for non-normal data), Xbar-R, Xbar-S, I-MR, P, NP, C, U, Laney, EWMA and CUSUM control charts with tests 1 to 8, attribute capability (% defective, DPU, Z and PPM), G and T charts for rare events and the multi-vari chart with run chart; shortcuts to the histogram and the simple run chart.

Cp and Cpk capability

Paste measurements (single column, subgroups or ID) or enter mean and standard deviation: Cp, CPL, CPU, Cpk, Pp, Ppk, Cpm with 95% CI, observed and expected PPM, Z.Bench, control charts, Box-Cox, Johnson, Weibull and lognormal, and the payoff of reducing variation.

Cp, Cpk, PPM, sigma level

Control charts

Shows whether a process is stable over time, separating normal variation from signals that something changed and needs investigating. Paste measurements to build Xbar-R, Xbar-S, I-MR, I-MR-R/S, P, NP, C, U, Laney P′/U′, EWMA or CUSUM charts with tests 1 to 8, stages, historical limits, unequal subgroups and the within sigma for Cpk.

X̄-R, I-MR, P, U, EWMA, tests 1–8

Attribute capability New

Measures process capability when the result is not a measurement but good/bad parts or a number of defects. For pass/fail characteristics or defect counts: paste the samples and get % defective or DPU with an exact confidence interval, PPM, process Z, P or U chart with tests, cumulative plot with confidence bounds, rate × sample size, histogram, report card and how many more parts to inspect to prove the target.

% defective, Z, DPU

G and T charts (rare events) New

Tracks whether rare defects, breakdowns or accidents are becoming more or less frequent by measuring the interval between them. For rare events, where a P or U chart would show almost only zeros: paste the event dates or the amounts between them and get the G (geometric) or T (Weibull or exponential) chart with probability limits, tests for special causes, cumulative events against expected, distribution fit, report card and annual cost.

Time between rare events

Multi-vari & run chart New

Helps find where the variation of a measurement comes from before hunting for the cause. Paste measurements with up to 4 factors (position on the part, part, hour, shift) and see the multi-vari chart with means connected by level and each family’s share of the variation; or analyze data order on the run chart, with clustering, mixtures, trend and oscillation tests.

Families of variation, run chart

Also useful

Histogram New

A histogram shows how the measurements of one characteristic are spread: where the center is, how much they vary and whether they fit within the specification limits. It is the first tool to understand a process before computing Cpk or changing settings. Paste measurements from Excel and get a histogram with automatic or adjustable bins, normal curve, mean and ±3s, specification limits with % out, a dot plot for small samples, overlaid, stacked or paneled groups, a plain-language reading of the shape and a frequency table.

Shape, bins, % out

Run chart New

A run chart shows a measure over time and answers whether it really changed or just wobbled by chance, without advanced statistics. It is the simplest way to prove whether an improvement worked. Paste a measure in time order (daily scrap, setup time, complaints per week) and the page draws the run chart with the median, goal and limits, highlights shifts of 6 or more points and trends of 5 or more by itself and counts the runs with the Provost and Murray table, explaining each signal in plain language.

Median, shifts, trends