LIVE TOOL

Control charts

I-MR, X̄-R and X̄-S charts with tests for special causes, from measurements pasted from Excel or CSV.

Input

Data layoutAutoOne column is read as individual values, several columns as subgroups.Individual valuesOne column, one measurement per row: use it when parts are measured one at a time.SubgroupsOne row per subgroup, columns are its measurements: use it when e.g. 5 parts are taken together every hour.

Example dataReplace with your own measurements

Measurements

Paste, open a CSV, TSV, TXT or XLSX file (up to 20 MB), or drop it on the field. Files are read in this browser only.

10,01
10,02
9,99

Individual values
1 column

10,01  10,02  9,99
10,00  10,03  9,98

Subgroups
1 row = 1 subgroup

Columns: tab, ; or ,
Decimals: 12,5 or 12.5

Layout: Subgroups · 25 rows × 5 columns · detected automatically
Read as: tab-separated · decimal comma · 25 subgroups of 5 (one per row), 125 values

ColumnsDecimal

Data as understood — first 10 of 25 subgroups
Subgroup	x1	x2	x3	x4	x5
Subgroup 1	11,984	11,972	12,015	12,004	12,004
Subgroup 2	12,010	11,996	11,987	12,002	11,976
Subgroup 3	11,995	11,988	12,007	12,009	11,951
Subgroup 4	11,982	12,012	12,005	11,980	12,004
Subgroup 5	11,990	11,996	11,997	11,966	11,983
Subgroup 6	11,993	11,959	11,988	12,009	11,974
Subgroup 7	12,029	11,970	12,003	11,974	11,983
Subgroup 8	11,999	11,987	11,984	11,999	11,993
Subgroup 9	11,984	11,962	12,012	11,997	11,991
Subgroup 10	11,988	11,980	11,962	11,990	12,001

+15 more subgroups

ChartChart type

Auto: one column → I-MR; subgroups of up to 8 → X̄-R; larger subgroups → X̄-S.

Show

Control limitsFrom the data (Phase I)Mean and σ are estimated from these measurements: use it to check whether the process was stable.Historical values (Phase II)Mean μ and σ come from earlier stable data: use it to monitor new measurements.

μ (mean)

σ (process)

Freeze limits fromN (baseline)

Live monitoring

Watch A file A folder

Check every (s, 1–60)

Sound on a new signal

Not watching. Choose a file or folder.

A file is read when its size and time have not changed for two checks; rows are added to the data above. The browser remembers your choice: after a reload, one click resumes watching.

Tests for special causes

1 1 point more than 3σ from the center line2 9 points in a row on the same side of the center line3 6 points in a row, all increasing or all decreasing4 14 points in a row, alternating up and down5 2 out of 3 points more than 2σ from the center line (same side)6 4 out of 5 points more than 1σ from the center line (same side)7 15 points in a row within 1σ of the center line (either side)8 8 points in a row more than 1σ from the center line (either side)

Tests 5–8 use the σ zones and apply to the mean / individuals chart; the range charts (R, S, MR) use tests 1–4.

Check capability

Runs in this browser. Data is not uploaded or stored.

Results

1 out-of-control signal

X̄-R · auto: subgroups of up to 5 (n ≤ 8) · limits from the data · mean 12,0071 · σ 0,0175242 (R̄ / d2, 25 subgroup ranges)

PointSignal (test number)Center lineUCL / LCL1σ, 2σ, 3σ zones

Out-of-control signals
Subgroup	Chart	Test	Description
Subgroup 21	X̄	1	1 point more than 3σ from the center line

Limits
Chart	LCL	CL	UCL
X̄ — subgroup mean	11,9836	12,0071	12,0307
R — subgroup range	0	0,04076	0,086187

Download offline versionSingle HTML file · v1.9 · 578 KB · works without internet

Method

Chart type, Auto: one value per row → I-MR; subgroups of up to 8 values → X̄-R; larger subgroups → X̄-S (the largest subgroup decides). Rows with one value each are charted as individual values.
σ estimate (Minitab defaults): I-MR: MR̄ / d2(2) with moving ranges of length 2. X̄-R: Rᵢ / d2(nᵢ) over subgroups with at least 2 values, weighted by fᵢ = d2(nᵢ)² / d3(nᵢ)² (Minitab’s R̄ method), which is R̄ / d2 when all subgroups have the same size. X̄-S: sᵢ / c4(nᵢ) weighted by hᵢ = c4(nᵢ)² / (1 − c4(nᵢ)²), which is S̄ / c4 for equal sizes.
Limits are 3σ of the plotted statistic. Mean chart: mean ± 3σ / √nᵢ, so unequal subgroups give limits that vary from subgroup to subgroup. R chart: d2σ ± 3 d3σ; S chart: c4σ ± 3σ√(1 − c4²); MR chart: d2(2)σ ± 3 d3(2)σ. A lower limit below 0 on a dispersion chart is set to 0.
Center line of the mean chart is the mean of all measurements. Phase II uses the μ and σ you enter for both charts.
Phase I and Phase II: in Phase I the limits are estimated from the data shown, so every new point also moves the limits; use it to judge whether a process was stable. In Phase II the limits come from a stable baseline and stay fixed, so new points are judged against them. Freeze limits takes μ and σ from the first N subgroups (25 by default) or from all data so far with the Phase I estimates above, switches to Phase II and fixes the chart type; the frozen values are saved in the settings file. Changing μ, σ, the chart type or going back to Phase I ends the freeze.
Live monitoring (Chrome and Edge, File System Access API) reads a file that a test stand appends rows to, or a folder where every new file (matching a pattern such as *.csv) is one subgroup or adds its rows. Changes are found by the browser's change notifications (FileSystemObserver) where available, otherwise by checking every 1–60 s (5 s by default). A file is read only after its size and time stayed the same for two checks, so a half-written file is never read; every file read is remembered by name, time and size and never read twice (a file appended to adds only its new rows). Files go through the same parser, encodings and “Read as” choices as a paste. Rows found when watching starts are history and raise no alert; a new out-of-control signal afterwards shows a banner, “(!)” in the page title and, if chosen, a short sound.
Monitoring limits: the page must stay open (a background tab may be checked less often by the browser), the browser asks for permission to read the file or folder, and files are only read, never changed. Sub-folders are not watched. In a folder, files are taken oldest first by their time. The website remembers the chosen file or folder in this browser (IndexedDB, the handle only, never the data); after a reload one click and the browser’s permission resume watching, reading the source from the start. Nothing is sent anywhere.
Tests follow the Nelson / Minitab numbering with Minitab's fixed parameters: 1 point beyond 3σ; 9 in a row on one side; 6 in a row rising or falling; 14 in a row alternating; 2 of 3 beyond 2σ (same side); 4 of 5 beyond 1σ (same side); 15 in a row within 1σ; 8 in a row beyond 1σ. Minitab's default is test 1 only; the others are switched on one by one. The range charts use tests 1–4 only.
Flagged point: the point that completes the pattern, and every later point of the same run that still fits it. Runs and windows do not cross an empty row.
Conclusion: “In control” when no enabled test fires, otherwise the number of signals (a point that fails two tests counts twice).
Limits estimated from fewer than 20 points are unreliable, and control charts assume the measurements were taken in time order. “Check capability” and “Check stability” pass the pasted data between the two tools in this browser tab; nothing is sent to a server.
Files: CSV, TSV and TXT are read as if pasted (UTF-8, UTF-16, otherwise Windows-1257). XLSX: choose the sheet and the columns or a cell range; formula cells use the value Excel last saved, dates are kept as text. Files up to 20 MB are read in this browser only and never uploaded.
XLSX files are read with SheetJS Community Edition 0.20.3, Apache License 2.0 (license), loaded only when an Excel file is opened or created.