Control chart rules poster (when to react)

A control chart shows whether a process is stable. Points inside the limits that wander at random are common cause variation: leave the process alone. Certain patterns signal a special cause worth finding: a point beyond a limit, runs on one side, trends. This poster draws the four Western Electric rules and two of Lloyd Nelson's tests, says what to do when one fires, and reminds the team that control limits come from the process, not from the drawing.

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Download PNG (300 dpi)2550 x 3300 px, prints at 8.5 x 11 in · 468 KB · no form

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Control chart rules poster — 24 x 36 in18 x 24 inA2A3LetterA4PNG 300 dpi

The words on the poster

Control chart: when to react

React to a signal. Leave a stable process alone.

1. One point outside a limit Beyond the upper or lower control limit.
2. Two of three near a limit Beyond 2 sigma, on the same side.
3. Four of five off centre Beyond 1 sigma, on the same side.
4. Eight in a row on one side All above, or all below, the centre line.
5. Six in a row rising or falling Each point higher, or lower, than the last.
6. Fourteen alternating Up, down, up, down: two streams mixed?

A rule fires: stop, find what changed, contain suspect parts, note it on the chart. No signal: don't adjust.

Rules 1 to 4: Western Electric (1956). Rules 5 and 6: Lloyd S. Nelson (1984). Sigma: one standard deviation. Control limits come from the process data, not the drawing.

On the floor

How to use it

Putting the Control chart rules poster (when to react) poster to work

1
Post it next to every control chart kept at a machine.
2
Agree which rules your plant uses before you print: many use rules 1 to 4 only.
3
When a rule fires, write what you found on the chart at that point.
4
Pair it with the free control chart template and out-of-control action plan.

Where the poster goes and how to teach with it, in the order to try them.

Which size to print

24 x 36 in or A2: a main wall or team board, read from a few metres away.
18 x 24 in or A3: a station or notice board. The A3 file also fits 11 x 17 in paper.
Letter or A4: a clipboard, binder or handout, on any office printer.

Every PDF is vector, so it stays sharp at full size. Nothing runs to the edge of the page, so no bleed is needed.

Sources and notes

Western Electric Company, Statistical Quality Control Handbook (1956): rules 1 to 4, with zones at one, two and three standard deviations.
Lloyd S. Nelson, "The Shewhart Control Chart: Tests for Special Causes", Journal of Quality Technology 16(4), 1984: trend and alternating tests.