Build a c chart

Example: glass-panel defects

An inspector counts scratches, pits and inclusions on 40 glass panels. Every panel has the same 1.00 m² inspected area and is checked under the same conditions.

Download the glass-panel example (CSV)

This is the same example used in Help. panel_id identifies each panel; surface_defects counts separate defects, so one panel can contribute several. inspected_area_m2 records the equal inspection area.

1. Create the chart workspace

In the sidebar, open Process control, choose c Chart, and name the analysis. Select New blank worksheet and Create analysis.

2. Import the data

On Worksheet, choose Import. Select the downloaded file or paste its contents. Set the delimiter to Comma, use Decimal dot, and check First row contains column names. Preview the import, then choose Import into worksheet. Keep the rows in collection order.

3. Assign the input columns

On Inputs, assign panel_id to Subgroup label and surface_defects to Number of nonconformities, selecting each from the column picker. Leave inspected_area_m2 as context in the worksheet; the c chart uses equal-area counts.

Open Western Electric / AIAG rules. Leave all five optional rules On: 7-point trend, 6 on one side, 14 alternating, 2 of 3 beyond 2σ and 4 of 5 beyond 1σ.

c Chart: Inputs with the example’s assignments and settings — Panel labels, surface-defect counts and all five optional signal rules on Inputs. View full-size image (opens in a new tab)

4. Run analysis

Choose Run analysis, then open Results.

5. Interpret results

Understand each point
Each point counts separate surface defects on one glass panel. A panel can contain several defects. Every panel has the same 1.00 m² inspected area.
Compare the counts with the limits
The average is 8.075 defects per panel. GLS36, GLS38, GLS39 and GLS40 cross the upper limit of 16.600. The lower limit is zero.
Separate surface defects on 40 equal-area panels. A panel may contain several defects. View full-size chart (opens in a new tab)
Read the highlighted points
Some highlighted points belong to patterns inside the limits, and several rules can flag one panel. In the signal-details table, returned index 35 identifies GLS36 (the 36th panel); indices start at 0. Use that ID to inspect the source record. Signal rows do not count separate defective panels.
Decide what to investigate
Review defect types and inspection conditions for GLS36, GLS38, GLS39 and GLS40. Confirm that the inspected area and defect criteria stayed the same. The chart shows unusual counts; it does not identify what caused them.

More details: read each result section

Complete result tables use six significant digits, as in Help.

c chart summary

Count every surface defect: a panel can have more than one. Equal inspection area and a consistent defect definition make counts comparable. This is not a count of nonconforming panels.

c chart summary · 8 rows
Statistic / setting	Value
Subgroups (k)	40
Average nonconformity count (c̄)	8.075
Beyond-limit detection	On
7-point trend	On
6 on one side	On
14 alternating	On
2 of 3 beyond 2σ	On
4 of 5 beyond 1σ	On

The c chart assumes a constant area of opportunity.

c values, control limits and zones

Each row lists the panel’s defect count and limits. Use GLS labels to inspect the source panel. Count defects rather than nonconforming panels and confirm equal inspection opportunity.

c values, control limits and zones · 40 rows
Subgroup	Label	c	CL	UCL	−1σ	+1σ	−2σ	+2σ	Signals
1	GLS01	8	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
2	GLS02	9	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
3	GLS03	7	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
4	GLS04	5	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
5	GLS05	6	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
6	GLS06	9	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
7	GLS07	8	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
8	GLS08	11	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
9	GLS09	4	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
10	GLS10	4	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
11	GLS11	6	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
12	GLS12	6	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
13	GLS13	9	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
14	GLS14	8	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
15	GLS15	11	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
16	GLS16	3	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side
17	GLS17	8	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side, 6 on one side
18	GLS18	6	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side, 6 on one side, 6 on one side
19	GLS19	3	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side, 6 on one side, 6 on one side
20	GLS20	5	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side, 6 on one side, 6 on one side
21	GLS21	6	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side, 6 on one side, 6 on one side
22	GLS22	6	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side, 6 on one side
23	GLS23	6	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side
24	GLS24	9	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
25	GLS25	9	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
26	GLS26	8	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
27	GLS27	7	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
28	GLS28	1	8.075	16.6	5.23335	10.9167	2.39169	13.7583	2 of 3 beyond 2σ, 2 of 3 beyond 2σ, 4 of 5 beyond 1σ
29	GLS29	1	8.075	16.6	5.23335	10.9167	2.39169	13.7583	2 of 3 beyond 2σ, 2 of 3 beyond 2σ, 4 of 5 beyond 1σ
30	GLS30	3	8.075	16.6	5.23335	10.9167	2.39169	13.7583	4 of 5 beyond 1σ
31	GLS31	9	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
32	GLS32	5	8.075	16.6	5.23335	10.9167	2.39169	13.7583	4 of 5 beyond 1σ
33	GLS33	6	8.075	16.6	5.23335	10.9167	2.39169	13.7583	None
34	GLS34	9	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side
35	GLS35	12	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side, 6 on one side, 4 of 5 beyond 1σ
36	GLS36	22	8.075	16.6	5.23335	10.9167	2.39169	13.7583	Beyond 3σ, 6 on one side, 6 on one side, 2 of 3 beyond 2σ, 4 of 5 beyond 1σ, 4 of 5 beyond 1σ
37	GLS37	10	8.075	16.6	5.23335	10.9167	2.39169	13.7583	6 on one side, 6 on one side
38	GLS38	18	8.075	16.6	5.23335	10.9167	2.39169	13.7583	Beyond 3σ, 6 on one side, 6 on one side, 2 of 3 beyond 2σ, 2 of 3 beyond 2σ, 2 of 3 beyond 2σ, 4 of 5 beyond 1σ, 4 of 5 beyond 1σ
39	GLS39	19	8.075	16.6	5.23335	10.9167	2.39169	13.7583	Beyond 3σ, 6 on one side, 6 on one side, 2 of 3 beyond 2σ, 2 of 3 beyond 2σ, 4 of 5 beyond 1σ, 4 of 5 beyond 1σ
40	GLS40	21	8.075	16.6	5.23335	10.9167	2.39169	13.7583	Beyond 3σ, 6 on one side, 2 of 3 beyond 2σ, 4 of 5 beyond 1σ

Control chart signal details

Each row names an inspection index or label and a rule. Beyond limits identifies a crossing; other rules flag patterns that may stay inside the limits. Several rules may flag the same sample. These entries identify inspections to investigate, not the number of defective panels.

Control chart signal details · 57 rows
Index (as returned)	Chart	Rule
15	c	6 on one side
16	c	6 on one side
16	c	6 on one side
17	c	6 on one side
17	c	6 on one side
17	c	6 on one side
18	c	6 on one side
18	c	6 on one side
18	c	6 on one side
19	c	6 on one side
19	c	6 on one side
19	c	6 on one side
20	c	6 on one side
20	c	6 on one side
20	c	6 on one side
21	c	6 on one side
21	c	6 on one side
22	c	6 on one side
27	c	2 of 3 beyond 2σ
27	c	2 of 3 beyond 2σ
27	c	4 of 5 beyond 1σ
28	c	2 of 3 beyond 2σ
28	c	2 of 3 beyond 2σ
28	c	4 of 5 beyond 1σ
29	c	4 of 5 beyond 1σ
31	c	4 of 5 beyond 1σ
33	c	6 on one side
34	c	4 of 5 beyond 1σ
34	c	6 on one side
34	c	6 on one side
35	c	2 of 3 beyond 2σ
35	c	4 of 5 beyond 1σ
35	c	4 of 5 beyond 1σ
35	c	6 on one side
35	c	6 on one side
35	c	Beyond 3σ
36	c	6 on one side
36	c	6 on one side
37	c	2 of 3 beyond 2σ
37	c	2 of 3 beyond 2σ
37	c	2 of 3 beyond 2σ
37	c	4 of 5 beyond 1σ
37	c	4 of 5 beyond 1σ
37	c	6 on one side
37	c	6 on one side
37	c	Beyond 3σ
38	c	2 of 3 beyond 2σ
38	c	2 of 3 beyond 2σ
38	c	4 of 5 beyond 1σ
38	c	4 of 5 beyond 1σ
38	c	6 on one side
38	c	6 on one side
38	c	Beyond 3σ
39	c	2 of 3 beyond 2σ
39	c	4 of 5 beyond 1σ
39	c	6 on one side
39	c	Beyond 3σ

Endpoint signal indices start at 0; chart subgroup numbers start at 1.

6. Create a report

Keep the c control chart, summary, panel values and limits, and signal details. State the 1.00 m² inspection area and the defect criteria. Record what you checked in GLS36, GLS38, GLS39 and GLS40.

Choose Add to report from the completed run. Open Choose individual items and advanced options to select tables and charts, then choose Add to draft. Hidden items stay in the saved analysis.

Name the report and add the purpose of the study and your interpretation. Choose Save, review Preview, then use Export → Download HTML. The example below contains the full selected content, including results beyond one screen.

Complete native output for this Help example, including applicable tables, charts and run notes. Report numbers use the app’s displayed precision. Exported charts are static. On narrow screens, scroll wide charts and tables sideways.

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