Control chart (SPC)
Statistical process control charts — I-MR, X̄-R, X̄-S, p, np, c and u — with the centre line and control limits computed from the data by the standard unbiasing constants (d2, d3, c4, A2, A3, B3, B4, D3, D4), never typed in. All eight Nelson rules run over the plotted series and every violation is marked and listed, and process capability (Cp, Cpk, Pp, Ppk) is computed when specification limits are given. A chart whose limits were guessed is not a control chart.
In the same space
Most users come to Control chart (SPC) from Minitab control charts, JMP, SPC for Excel or InfinityQS. flowss runs this engine in the browser — no install, shareable via URL, exportable to PNG / SVG / PDF / source.
Syntax at a glance
chart xbar-r
spec lsl: 495 usl: 505
subgroup 500.1 499.8 500.4 500.0
subgroup 500.9 501.2 500.7 500.5Paste this in the Studio code pane to see Control chart (SPC) render live. The full grammar is at the upstream-docs link above.
Sample templates
All 13 →Twenty-two subgroups of four bottles from a rotary filler, with X̄ and R limits from A2/D3/D4 and Cp/Cpk/Pp/Ppk against a 495–505 ml specification; a late head adjustment shows up as rule 1, 5 and 6 signals.
Fourteen subgroups of nine mouldings with limits from A3/B3/B4, showing a tool-wear drift that rules 1, 3 and 5 catch and a Cpk of 0.90 against a 12.40–12.60 mm print tolerance.
Twenty-one months of CLABSI counts over a varying number of catheter-days, plotted as infections per 1,000 catheter-days with limits that step with the exposure and a rule-2 run confirming the insertion-bundle rollout worked.
Twenty-one days of abandoned calls against a daily volume that swings from 780 to 1,540, giving stepped binomial limits around a 5.1% centre line and isolating the storm-day spike as the only genuine special cause.
Twenty-four consecutive vehicle bodies inspected for weld defects on a constant area of opportunity, with Poisson limits at c̄ ± 3√c̄ and one body beyond the upper limit after a robot tip-dress was missed.
Sixteen release batches assayed in triplicate by HPLC, showing a stable process centred 0.33% above label claim with Cp 1.63 and Cpk 1.52 against the 95–105% compendial specification.
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