Build a Z-MR chart

Compare measurements from different products on a standardized scale.

Guides · Process control (SPC) · 4 min read

Example: three spacer products

A machining cell alternates among three spacer products in 18 runs. Five parts are measured per run, giving 90 length measurements.

Download the spacer-length example (CSV)

This is the same example used in Help. product_id identifies SP-25, SP-40 or SP-60; run_id identifies each production run; length_mm contains measured length in mm. Each product’s mean and standard deviation are estimated from these data.

1. Create the workspace

In the sidebar, open Process control, choose Z-MR 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 product_id to Part ID, run_id to Run ID, and length_mm to Measurements, selecting each from the column picker. Keep the complete sequence in collection order.

4. Set the product baselines

Choose Per part for both Standard deviation method and Centering method. Enter 2 in Moving range length and choose Average MR under Moving-range statistic.

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.

Z-MR Chart: Inputs with the example’s assignments and settings
Product and run labels, length measurements, per-part estimates and enabled rules on Inputs. View full-size image (opens in a new tab)

5. Run analysis

Choose Run analysis, then open Results.

6. Interpret results

  1. Understand the standardized scale

    For each product, the app subtracts its estimated mean from each length and divides by its estimated standard deviation. The result is Z. A Z of 3 is three estimated standard deviations above that product’s mean; it is not 3 mm above target.

  2. Check changes between neighbors

    The moving-range chart shows changes between consecutive Z values. No points cross its upper limit of 3.685. The first reading has no moving range. Ranges continue across run boundaries, so also check product transitions.

    Moving range of Z
    Moving ranges of standardized measurements. Ranges continue across run boundaries. View full-size chart (opens in a new tab)
  3. Check the Z values

    Observation 69 is product SP-40, run RUN14, sample 4, measuring 40.108 mm. Its Z crosses the upper limit of +3. Pattern rules also flag 25–31 and 63–70. Use product and run IDs to inspect the original records: a signal is relative to the estimated product baseline, not a failed length specification.

    Standardized individuals chart (Z)
    Standardized measurements for 90 parts. Z has no measurement unit. View full-size chart (opens in a new tab)
  4. Check the product baselines

    The estimated means are 24.9965, 40.0030 and 60.0087 mm for SP-25, SP-40 and SP-60. Their estimated standard deviations are about 0.02204, 0.0324 and 0.06184 mm. These estimates use the current data, including the flagged readings.

  5. Decide what to investigate

    Check observation 69 against its product baseline and the neighboring run records. Review each product’s reference separately before ongoing monitoring. The charts locate unusual standardized behavior; they do not identify a shared cause across products.

More details: read each result section

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

Mean and sigma breakdowns

Estimated means are 24.9965, 40.0030 and 60.0087 mm for SP-25, SP-40 and SP-60. Their sigmas are approximately 0.02204, 0.0324 and 0.06184 mm. These are estimates from the current observations, not historical reference parameters.

Mean and sigma breakdowns · 6 rows
ParameterPart / run / poolEstimate
Mean (μ)SP-2524.9965
Mean (μ)SP-4040.003
Mean (μ)SP-6060.0087
Sigma (σ)SP-250.0220408
Sigma (σ)SP-400.032404
Sigma (σ)SP-600.0618427

Z–MR summary

The 90 observations use per-part mean and sigma estimates with average moving ranges of length 2. Identity transform keeps the original measurements on their measured scale before standardization.

Z–MR summary · 6 rows
Statistic / settingValue
Observations90
Mean strategyby part
Sigma strategyby part
Moving-range span2
Moving-range statisticmean
Transformidentity

Z and moving-range limits

Z and MR of Z are dimensionless. A Z of 3 means three estimated product sigmas above that product’s mean; it does not mean 3 mm above target.

Z and moving-range limits · 2 rows
ChartCLLCLUCL−1σ+1σ−2σ+2σ
Z0-33-11-22
MR of Z1.12803.685————

Standardized values and moving ranges

Each row connects an observation with its part, run, original measurement, standardized Z and moving range. Use these identities to trace observation 69 to its source row. Only the first MR is missing with length 2; ranges continue across run transitions.

Standardized values and moving ranges · 90 rows
ObservationPartRunOriginal valueZMR of ZZ signalsMR signals
1SP-25RUN0125.0070.476388—None—
2SP-25RUN0124.945-2.336572.81296NoneNone
3SP-25RUN0125.0070.4763882.81296NoneNone
4SP-25RUN0124.994-0.1134260.589814NoneNone
5SP-25RUN0125.0150.8393510.952777NoneNone
6SP-40RUN0239.982-0.6480681.48742NoneNone
7SP-40RUN0240.0190.4937661.14183NoneNone
8SP-40RUN0239.975-0.8640911.35786NoneNone
9SP-40RUN0240.003-2.19276e-130.864091NoneNone
10SP-40RUN0240.0080.1543020.154302NoneNone
11SP-60RUN0359.955-0.8677921.02209NoneNone
12SP-60RUN0360.0741.056441.92424NoneNone
13SP-60RUN0360.1552.366221.30977NoneNone
14SP-60RUN0360.0110.03773012.32849NoneNone
15SP-60RUN0359.922-1.40141.43913NoneNone
16SP-25RUN0425.0211.111572.51298NoneNone
17SP-25RUN0424.985-0.5217591.63333NoneNone
18SP-25RUN04250.1587960.680555NoneNone
19SP-25RUN0424.987-0.4310180.589814NoneNone
20SP-25RUN0425.0432.109722.54074NoneNone
21SP-40RUN0540.0230.6172081.49251NoneNone
22SP-40RUN0539.941-1.913342.53055NoneNone
23SP-40RUN0539.988-0.4629061.45044NoneNone
24SP-40RUN0540.0461.3271.7899NoneNone
25SP-40RUN0539.975-0.8640912.191096 on one sideNone
26SP-60RUN0660.002-0.10780.756296 on one side, 6 on one sideNone
27SP-60RUN0659.97-0.6252420.5174416 on one side, 6 on one sideNone
28SP-60RUN0659.989-0.3180110.3072316 on one side, 6 on one sideNone
29SP-60RUN0660.001-0.123970.1940416 on one side, 6 on one sideNone
30SP-60RUN0659.982-0.4312010.3072316 on one side, 6 on one sideNone
31SP-25RUN0724.98-0.748610.3174096 on one sideNone
32SP-25RUN0725.021.06621.81481NoneNone
33SP-25RUN0724.99-0.2949071.36111NoneNone
34SP-25RUN0725.010.6124990.907406NoneNone
35SP-25RUN0725.0040.3402770.272222NoneNone
36SP-40RUN0839.943-1.851622.1919NoneNone
37SP-40RUN0839.961-1.296140.555487NoneNone
38SP-40RUN0839.972-0.9566720.339464NoneNone
39SP-40RUN0840.0280.7715091.72818NoneNone
40SP-40RUN0839.937-2.036782.80829NoneNone
41SP-60RUN0959.95-0.9486431.08814NoneNone
42SP-60RUN0960.0580.7977221.74636NoneNone
43SP-60RUN0960.0380.4743210.323401NoneNone
44SP-60RUN0960.0330.3934710.0808502NoneNone
45SP-60RUN0960.0110.03773010.355741NoneNone
46SP-25RUN1024.9970.02268520.0150449NoneNone
47SP-25RUN1024.965-1.429171.45185NoneNone
48SP-25RUN1024.993-0.1587961.27037NoneNone
49SP-25RUN1025.0211.111571.27037NoneNone
50SP-25RUN1024.977-0.8847211.99629NoneNone
51SP-40RUN1139.94-1.94421.05948NoneNone
52SP-40RUN1139.946-1.759040.185162NoneNone
53SP-40RUN1139.981-0.6789281.08011NoneNone
54SP-40RUN1140.001-0.06172080.617208NoneNone
55SP-40RUN1140.0431.234421.29614NoneNone
56SP-60RUN1260.0250.2641110.970304NoneNone
57SP-60RUN1259.972-0.5929020.857012NoneNone
58SP-60RUN1260.1071.590052.18296NoneNone
59SP-60RUN1260.0160.118581.47147NoneNone
60SP-60RUN1259.864-2.339272.45785NoneNone
61SP-25RUN1324.979-0.7939811.54529NoneNone
62SP-25RUN1324.994-0.1134260.680555NoneNone
63SP-25RUN1325.0140.7939810.9074066 on one sideNone
64SP-25RUN1325.0010.2041660.5898146 on one side, 6 on one sideNone
65SP-25RUN1325.0010.20416606 on one side, 6 on one side, 6 on one sideNone
66SP-40RUN1440.0511.48131.277136 on one side, 6 on one side, 6 on one side, 4 of 5 beyond 1σNone
67SP-40RUN1440.0571.666460.1851626 on one side, 6 on one side, 6 on one side, 4 of 5 beyond 1σNone
68SP-40RUN1440.0350.9875320.6789286 on one side, 6 on one side, 6 on one sideNone
69SP-40RUN1440.1083.240342.25281Beyond 3σ, 6 on one side, 6 on one side, 2 of 3 beyond 2σ, 2 of 3 beyond 2σ, 4 of 5 beyond 1σNone
70SP-40RUN1440.0922.746570.4937666 on one side, 2 of 3 beyond 2σ, 2 of 3 beyond 2σ, 4 of 5 beyond 1σNone
71SP-60RUN1559.994-0.2371612.98373NoneNone
72SP-60RUN1560.004-0.07546020.1617NoneNone
73SP-60RUN1560.0721.02411.09956NoneNone
74SP-60RUN1560.0290.3287910.695312NoneNone
75SP-60RUN1559.972-0.5929020.921693NoneNone
76SP-25RUN16250.1587960.751698NoneNone
77SP-25RUN1624.97-1.202311.36111NoneNone
78SP-25RUN1624.9990.1134261.31574NoneNone
79SP-25RUN1624.982-0.657870.771295NoneNone
80SP-25RUN1624.994-0.1134260.544444NoneNone
81SP-40RUN1740.0661.94422.05763NoneNone
82SP-40RUN1739.98-0.7097892.65399NoneNone
83SP-40RUN1739.977-0.802370.0925811NoneNone
84SP-40RUN1740.0361.018391.82076NoneNone
85SP-40RUN1739.976-0.833231.85162NoneNone
86SP-60RUN1859.924-1.369060.535834NoneNone
87SP-60RUN1860.1041.541542.91061NoneNone
88SP-60RUN1860.1131.687070.14553NoneNone
89SP-60RUN1859.925-1.352893.03997NoneNone
90SP-60RUN1859.988-0.3341811.01871NoneNone
  • Initial moving ranges are missing until a complete window is available.

Control chart signal details

Each row identifies an observation, chart and triggered rule. Observation 69 crosses the Z upper limit; patterns also flag 25–31 and 63–70. Multiple entries can concern one observation. A Z signal is relative to the estimated product baseline, not a failed length specification.

Control chart signal details · 39 rows
Observation / subgroupChartRule
25Z6 on one side
26Z6 on one side
26Z6 on one side
27Z6 on one side
27Z6 on one side
28Z6 on one side
28Z6 on one side
29Z6 on one side
29Z6 on one side
30Z6 on one side
30Z6 on one side
31Z6 on one side
63Z6 on one side
64Z6 on one side
64Z6 on one side
65Z6 on one side
65Z6 on one side
65Z6 on one side
66Z4 of 5 beyond 1σ
66Z6 on one side
66Z6 on one side
66Z6 on one side
67Z4 of 5 beyond 1σ
67Z6 on one side
67Z6 on one side
67Z6 on one side
68Z6 on one side
68Z6 on one side
68Z6 on one side
69Z2 of 3 beyond 2σ
69Z2 of 3 beyond 2σ
69Z4 of 5 beyond 1σ
69Z6 on one side
69Z6 on one side
69ZBeyond 3σ
70Z2 of 3 beyond 2σ
70Z2 of 3 beyond 2σ
70Z4 of 5 beyond 1σ
70Z6 on one side
  • Signal observations are displayed starting at 1.

7. Create a report

Keep Standardized individuals chart (Z) and Moving range of Z, together with the summary, Mean and sigma breakdowns, limits, standardized values and signal details. Record which product and run contain observation 69 and how each product baseline was estimated.

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.
View example report: Monitor standardized measurements across three spacer products

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