Home / Statistical Tools / Control Charts / Individuals / Options
Options¶
This page covers what is specific to the dialog behind the Individuals chart. That dialog is titled I-MR Chart, not Individuals Chart, because one dialog serves three ribbon entries. The parts shared by every control chart, the Data Selection window, the Data tab, and the analysis pane, are described once on Create Control Charts. What each option means statistically is on the Math Details page.
The Dialog¶
Above the tabs, a Chart: row of three radio buttons decides which panels are drawn: I-MR (both panels, the default when the dialog is opened from the I-MR ribbon entry), Individuals, and Moving Range. The ribbon entry Individuals opens this dialog with the Individuals radio already selected, and the title stays I-MR Chart. The choice only decides what is drawn: both panels are computed either way, unless you select Square root of MSSD on the Limits and Estimation tab, which removes the Moving Range panel altogether, and the worksheet is named after the variant rather than after the dialog, so this variant produces a sheet named Individuals Chart.
Selecting this variant also changes the Estimate Sigma group, silently. See Estimate Sigma below.
The Individuals variant has all four tabs, including Capability.
Data Tab¶
The slot lists are Measurement Columns and X-Axis Labels (Optional). See Create Control Charts for what each one does.
Three things are specific to this chart:
- There is no Subgroups group on this dialog. Every chart in the Charts as Individuals family reads one observation per row, so there is no subgroup mode to pick, no subgroup identifier column, and no subgroup size box. Each selected row is one plotted point.
- With no Subgroups group, each checked measurement column produces its own chart rather than another observation inside a shared point. Check three columns and you get three Individuals charts.
- Blank rows are not closed up. A blank empties its position on the chart. It also breaks the chain of consecutive observations behind the sigma estimate, whichever method is selected, because neither a moving range nor a successive difference is ever formed across a gap.
Limits and Estimation Tab¶
This tab carries six groups: Estimate Sigma, Transformation, and Historical Values on the left, and Control Limits, Estimate Limits From, and Split Control Limits on the right.
Control limits¶
The Control Limits group on the Limits & Estimation tab sets how the limits on every panel are obtained.
| Control | Type | Default | What it does |
|---|---|---|---|
| Shewhart | radio button | selected | The center line and the limits are computed from the data. |
| Manual | radio button | not selected | You type the limits yourself, one row per panel. |
| None | radio button | not selected | No limits are drawn. The points, the center line, the process statistics, and the outlier markers are all still produced. |
Manual is not offered on every chart and can be switched off by settings on other tabs. The availability table below covers both.
Choosing None also turns the out-of-control tests off. On a variable chart, blanking the limits blanks every test result as well, so no point is flagged, including by the tests that need only the center line. The zone lines checkbox is not greyed out when you choose None, but ticking it has no visible effect because there are no zone values to show.
Validation: none of the three radios can produce an invalid state, so there is no message.
Math: Control Limits and Zones.
Number of standard deviations (k)¶
| Control | Type | Default | Accepts |
|---|---|---|---|
| Number of standard deviations (k): | text box | 3 | any number greater than zero, with no upper bound |
This is how far the limits sit from the center line, measured in estimated standard deviations. Lower it and the chart flags more points; raise it and it flags fewer.
Editing k also changes the first out-of-control test. That test asks whether a point lies beyond k standard deviations from the center line, and it reads this same box. That is why it is the one test with no parameter of its own: k is its parameter.
It does not move the zone lines. On a variable chart the zone lines are drawn at one third and two thirds of the band, whatever k is, so with k set to 2 the line labelled 1 sigma actually sits at about two thirds of a sigma. The tests that count points inside and outside the zones move with the lines, so they change meaning too.
Where it is hidden. CUSUM has no k box. Its decision interval takes the place of a sigma multiplier.
Validation: blank, non-numeric, zero, and negative entries are all rejected, and the box snaps back to its previous value the moment it loses focus. There is no message, so it is easy to believe an entry was accepted when it was discarded.
Math: Control Limits and Zones.
Manual limits¶
Selecting Manual enables a grid with one row per panel and the column headings Panel, UCL, Center, and LCL. Each cell is a text box, all of them start blank, and any number is accepted.
Each row is judged on its own, and what you leave blank matters as much as what you fill in.
| What a row contains | What that panel does |
|---|---|
| All three values, with LCL below Center and Center below UCL | Your band is drawn in place of the computed one. |
| Nothing at all | That panel falls back to computed limits, even though Manual is selected. This is deliberate: it lets you set a location panel by hand and leave the dispersion panel to the software. |
| One or two of the three | The panel is replaced by a red message where its chart would have been. No chart is drawn for that panel. |
| All three, but not in increasing order | The same red message replaces the panel. |
There is no validation message. The dialog accepts a half-filled row without comment and Finish stays enabled, so the failure appears only in the finished worksheet. Check every row before you press Finish.
Values you type survive a switch away from Manual, but they do not act. Choosing Shewhart or None leaves the grid as you left it and stops it from affecting the run. Switching back to Manual makes those values live again.
Zones and tests follow the band you typed. The zone lines are placed at thirds of your band, computed separately above and below the center, so an asymmetric band gets asymmetric zones. The first out-of-control test means "outside the typed band" rather than any particular multiple of a sigma estimate.
The process statistics are still computed from the data. The mean and the sigma estimates continue to be estimated and continue to be reported in the summary table, even though they no longer draw the band.
Math: Control Limits and Zones.
On this dialog the grid has two rows, one for the Individuals panel and one for the Moving Range panel, and it is not filtered by the variant. Under the Individuals variant the Moving Range row is still shown. Anything entered in it is accepted and computed, but that panel is not drawn, so it has no visible effect. Fill the Individuals row, all three of its values, to fix the band on this chart by hand: a row with one or two of its three values entered loses that panel entirely.
The two rows are labelled Individuals and Moving Range, whichever variant is selected.
Historical (known) values¶
The Historical Values group lets you supply a number instead of estimating it, so the limits describe a process you have already characterized rather than the data in front of you. Every box is a text box, every box starts blank, and blank means estimate it from the data.
| Control | Type | Default | What it replaces |
|---|---|---|---|
| Mean: | text box | blank | the mean behind the center line |
| Standard deviation (overall): | text box | blank | the overall sigma |
| Standard deviation (within): | text box | blank | the within-subgroup sigma |
| Mean (between): | text box | blank | the mean of the subgroup means |
| Standard deviation (between): | text box | blank | the between-subgroup sigma |
Which boxes appear depends on the chart, because a box for a quantity the chart never uses would be misleading.
| Chart | Boxes shown |
|---|---|
| Xbar-R, Xbar-S, I-MR | Mean, overall, within |
| I-MR-R/S | all five |
| EWMA, CUSUM | Mean, within |
| Levey-Jennings | Mean, overall |
Behavior worth knowing:
- A supplied value wins, and it is applied last. The estimate is computed from the data first and then overwritten, so a First N baseline still selects which points fed the discarded estimate, and still governs anything you did not supply.
- One number can change two. Supplying a within sigma also redefines the between sigma, and supplying a between sigma redefines the sigma of the subgroup means, because the remaining quantity is back-solved from the data.
- A supplied sigma carries no degrees of freedom, so it gets no confidence interval in the capability output. A supplied mean affects no degrees of freedom.
- One value covers every phase. With split control limits on, the same supplied number applies to all phases; there is no per-phase historical value.
- A transformation discards them for that run. Turning on Box-Cox or Johnson greys out the whole group and the values are not used. What you typed reappears if you turn the transformation off.
Validation: none of these boxes is range-checked in the dialog. The one engine check is on Levey-Jennings, which refuses a supplied overall standard deviation that is not a positive number. Anywhere else an unusable value is accepted and shows up as an unusable chart.
Math: Process Sigma Estimation.
A historical mean together with manual limits¶
These two are not mutually exclusive on most charts, and the result differs by chart. None of the three behaviors is announced, so read the row for your chart before combining them.
| Charts | What happens |
|---|---|
| Xbar-R, Xbar-S, I-MR, I-MR-R/S | Both settings act, on different parts of the output. The chart draws the center line you typed in the manual grid, while the summary table reports the historical mean. The two disagree by design, so expect it rather than treating it as an error. |
| EWMA, CUSUM | The combination cannot arise. Manual limits are not offered on either chart, so a historical value is the only one of the two you can set. |
| Levey-Jennings | The combination is blocked in both directions. Entering any historical value greys out Manual, and selecting Manual greys out the whole Historical Values group. |
| p, np, Laney P', c, u, Laney U' | The historical box disappears when you select Manual and its value is ignored for that run, because nothing is estimated under manual limits. Switching back to Shewhart brings both the box and its effect back. |
What switches these options off¶
Four combinations of settings make an option on this tab unavailable. Every one of them acts the moment you type or select, and none of them shows a message, so it is worth knowing them before you go looking for a control that has greyed out.
| When this is set | This becomes unavailable |
|---|---|
| A Box-Cox or Johnson transformation | Manual limits. The radio greys out, and a Manual selection reverts to Shewhart. The Historical Values boxes are also ignored for that run. |
| Any split mode other than None, whether or not you have entered break points yet | Manual limits, in the same way. Selecting the mode is enough; the gate does not check whether the split produces anything. |
| A lower or upper specification limit on the Capability tab. A target alone does not do this. | First N subgroups under Estimate Limits From. The selection reverts to All subgroups. Levey-Jennings, EWMA, CUSUM and Z-MR have no Capability tab, so this gate cannot arise on them. |
| A transformation and a specification limit together | Split control limits. The whole Split Control Limits group greys out and the mode reverts to None. |
The specification-limit gate reads the two specification boxes only, so a Target: on its own leaves First N subgroups: selectable. That combination does not produce a chart: a target alone is enough to turn the capability calculation on, and the engine refuses to combine capability with a First N baseline, so the run stops with "Capability cannot be combined with a First-N baseline." Clear the target, or return Estimate Limits From to All subgroups.
Two chart-level rules sit alongside them: EWMA and CUSUM never offer manual limits at all, and Levey-Jennings treats manual limits and historical values as mutually exclusive, so entering either one greys out the other.
What Estimate Limits From (Baseline Estimation) does¶
It changes what the limits are estimated from. It never changes what is plotted. Every point always appears on the chart. Asking for the first 25 subgroups does not hide subgroup 26 onward. It means the center line and the control limits are computed from the first 25 subgroups and then drawn straight across the whole chart, so the later points are judged against the earlier baseline. That is the entire purpose of the setting: it is how you freeze a known-good period and watch what happens afterwards.
The same setting carries two labels. It is Estimate Limits From on the variable charts and Baseline Estimation on the attribute and rare-event charts, because those dialogs were written separately. The intent is identical, but the smallest count you may enter differs, and so do a few of the edge cases, so use the block written for this chart.
| Estimated from the selected points only | Computed from all the points regardless |
|---|---|
| The mean behind the center line | Every plotted value |
| The overall sigma | Each subgroup's own mean, range, and standard deviation |
| The within-subgroup sigma and everything it is built from | The minimum, the maximum, and the count |
| The between-subgroup sigma | The observed parts per million outside the specification |
| The moving-range estimates on an individuals chart | The histogram and the distribution fit |
| The estimated proportion or rate on an attribute chart | The out-of-control tests, which are applied to every point |
| The reported degrees of freedom | |
| The transformation itself |
Two of those rows surprise people:
- The transformation is fitted on the baseline too. A Box-Cox lambda or a set of Johnson parameters is fitted from the baseline points only and then applied to every row in the data. Change the baseline and you change the transformation, not just the limits.
- The degrees of freedom come from the baseline, so a short baseline widens the capability confidence intervals as well as changing the limits.
With split control limits on there is still only one count. It is reused inside every phase, capped at the length of that phase, so a phase shorter than the count simply uses all of its own points. The count never reaches across a phase boundary, and there is no way to give one phase a different baseline from another.
Math: Baseline and Limit Estimation.
Estimate Limits From¶
| Control | Type | Default | Accepts |
|---|---|---|---|
| All subgroups | radio button | selected | |
| First N subgroups: | radio button | not selected | |
| the count box beside it | text box | blank | a whole number of 5 or more. Its tooltip reads "Minimum 5 subgroups". |
The count is in plotted points, not in worksheet rows. On an individuals chart it counts points, and the moving ranges available inside that window are one fewer than the count at the default moving range length, fewer still if there are gaps.
Everything this control does when your entry is not usable, it does silently:
| What you do | What happens |
|---|---|
| Select First N subgroups: and leave the box blank | Exactly the same as All subgroups: every point estimates the limits. |
| Type a number below 5 | Raised to 5 as soon as the box loses focus. |
| Type a number larger than the data | Every point is used. |
| Leave a blank subgroup inside the window | It does not use up one of the N. The window reaches further into the data to find real subgroups. |
| Exclude a point as an outlier inside the window | The same: it does not use up one of the N. |
A specification limit switches this off. Type a lower or an upper specification limit on the Capability tab and First N subgroups: greys out and the selection reverts to All subgroups, because a frozen baseline and a capability calculation disagree about which data describes the process. Levey-Jennings, EWMA, CUSUM and Z-MR have no Capability tab, so this cannot arise on them. There is no message, and clearing the specification limit makes the radio available again.
A target on its own does not switch it off, and the combination then fails
The dialog gate reads the LSL: and USL: boxes only, so a Target: with both specification boxes empty leaves First N subgroups: selectable. It should not be. A target on its own is enough to turn the capability calculation on, and the engine refuses to combine any capability calculation with a First N baseline, so pressing Finish in that state produces no chart at all and the message "Capability cannot be combined with a First-N baseline."
To avoid it, either clear the Target: box or set Estimate Limits From back to All subgroups.
Every phase still needs at least five usable points. With split control limits on, one phase too short fails the whole analysis with a message instead of a chart, whatever this setting says.
Validation: nothing about this control is ever reported. The count is corrected in place and the analysis runs.
The control still says "subgroups" on this dialog, and this chart has none. The two radio buttons read All subgroups and First N subgroups: here exactly as they do on Xbar-R. On an Individuals chart the count is a count of plotted points, which is the same as a count of worksheet rows, so First N subgroups: 25 estimates the limits from the first 25 observations. Those 25 points supply at most 24 successive differences, and fewer if there is a gap among them.
Estimate Sigma, individual observations¶
With one observation per point there is no within-subgroup spread to work with, so the estimate comes from how much consecutive points differ.
| Control | Type | Default | What it uses |
|---|---|---|---|
| Average moving range | radio button | selected | the mean of the moving ranges |
| Median moving range | radio button | not selected | the median of the moving ranges, which is much less disturbed by one large jump |
| Square root of MSSD | radio button | not selected, and shown only on the charts that offer it | the mean of the squared successive differences |
| Moving range length: | text box | 2 | a whole number from 2 to 100 |
| Use Nelson moving-range correction | check box | unchecked | on or off |
Moving range length is how many consecutive points each moving range spans. It disappears when Square root of MSSD is selected, because that method always uses consecutive pairs and would ignore it. It is shown only on the dialogs that offer the individuals sigma methods; a subgrouped chart that uses a moving range internally does not expose it, and its length is fixed at 2.
Use Nelson moving-range correction repeatedly removes unusually large moving ranges before averaging them, so that a genuine upset does not inflate the limits that are meant to detect it. It is available only with Average moving range: choose another method and the tick is cleared without a message, and the checkbox greys out. It considers only the moving ranges inside the baseline window, so a First N baseline restricts it further.
Validation: a moving range length below 2 or above 100 is silently replaced by the nearest allowed value, and the box shows the corrected number. There is no message.
Math: Process Sigma Estimation and Moving Ranges.
This is the only variant of this dialog that offers Square root of MSSD, alongside Average moving range and Median moving range.
You do not arrive on MSSD. Opening the dialog from the Individuals ribbon entry leaves Average moving range selected, which is the method every chart in this family starts on. MSSD is forced only when you click the Individuals radio yourself inside an already open dialog. So the state you land in from the ribbon is average moving range, with Moving range length: visible and the Nelson correction available; the state you reach by clicking the radio is MSSD, with both of those gone.
Selecting MSSD also removes the Moving Range panel. The panel count follows the sigma method, not the variant: under MSSD the chart is a single Individuals panel, nothing is computed for a moving range panel, and the Moving Range row in the manual limits grid has no panel to apply to.
The variant changes the method for you, without a message. Three things happen silently:
- Selecting the Individuals variant switches the sigma method to Square root of MSSD.
- Leaving the Individuals variant switches it back to Average moving range, whatever you had chosen.
- Choosing Square root of MSSD clears the Use Nelson moving-range correction tick and hides the Moving range length: box, because that method always works on consecutive pairs.
So on this chart the Moving range length: box is not visible until you select one of the two moving range methods, and the Nelson correction is available only under Average moving range. None of the three changes is announced anywhere in the dialog, so check the Estimate Sigma group after you change the variant.
The unbiased-constants checkboxes¶
Every estimate of a standard deviation from small samples runs slightly low on average. These two checkboxes decide whether that small bias is corrected. They have different defaults, which is easy to miss.
| Control | Type | Default | What it changes |
|---|---|---|---|
| Use unbiased constants (within sigma) | check box | checked | the correction applied to the within-subgroup estimate |
| Use unbiased constants (overall sigma) | check box | unchecked | the correction applied to the overall estimate |
The within checkbox greys out for some methods, because it would do nothing. It has an effect only with Sbar, with the Pooled standard deviation, and with the Square root of MSSD. With Rbar, the Average moving range, and the Median moving range the correction is always part of the estimate, so the dialog disables the checkbox rather than pretending the choice exists.
The overall checkbox is never greyed out, and it is a small correction because it is applied over the whole data set. It never moves a drawn control limit on any chart: the one chart whose limits come from the overall estimate is Levey-Jennings, and that chart shows neither checkbox.
Levey-Jennings does not show either box, and ignores both. Its overall standard deviation is always the uncorrected form.
Validation: checkboxes cannot be invalid, so there is no message. When a correction factor does not exist for the size it would be evaluated at, the correction is skipped and the uncorrected value is reported rather than nothing.
Math: Process Sigma Estimation and Control Chart Constants.
On this chart the within checkbox is greyed out under the average and median moving range methods, because each of those applies its own constant already. It becomes live only under Square root of MSSD, where it divides the estimate by a tabulated correction factor and therefore moves both limits. Since the dialog opens on average moving range, the checkbox starts greyed and becomes live only once you select MSSD.
Transformation¶
A transformation replaces each measurement with a rescaled version of itself, chosen so the rescaled values sit closer to a normal distribution. Control charts assume a normal distribution and never fit any other one, so a transformation is the only remedy the product offers for skewed measurement data on a control chart.
| Charts | Transformation group box |
|---|---|
| Xbar-R, Xbar-S, I-MR, I-MR-R/S, EWMA, CUSUM | Offered |
| Levey-Jennings, Z-MR | Not offered. There is no control, and no transformation is applied. |
| p, np, Laney P', c, u, Laney U', G, T | Not offered. These charts plot counts, proportions, or waiting times and have their own distributions built in. |
Controls¶
The group box is headed Transformation.
| Label as shown | Control | Default | Valid entries | What it does |
|---|---|---|---|---|
| None | Radio button | Selected | n/a | The chart is built from the measurements as entered. |
| Use Johnson Transformation | Radio button | Not selected | n/a | Fits a Johnson family transformation. |
| Use Box-Cox Transformation | Radio button | Not selected | n/a | Fits a Box-Cox power transformation. All values used must be positive. |
| Use Optimal Lambda | Radio button | Selected as soon as Box-Cox is chosen | n/a | The power is fitted from your data. |
| Enter Custom Value | Radio button | Not selected | n/a | You supply the power instead of fitting it. |
| (lambda box) with the hint (-5 to 5) beside it | Text box, no label of its own | Empty | A number | The power to use. |
Hidden rather than disabled: the Use Optimal Lambda and Enter Custom Value buttons appear only while Use Box-Cox Transformation is selected, and the lambda box and its (-5 to 5) hint appear only while Enter Custom Value is selected. The Johnson transformation takes no parameters, so it reveals nothing.
Validation. The dialog does not check the lambda box against the range in the hint beside it, and it shows no message of any kind. The value you type is passed on as it stands, and the supported range is enforced further in, where the transformation is computed. The two shared math pages define the transformations and the range: Box-Cox Transformation and Johnson Transformation.
What a transformation affects¶
A transformation is not a display option. It changes the numbers the whole analysis is built from, so read the chart in transformed units afterwards.
| Affected | Not affected |
|---|---|
| The plotted points on every panel | Which points appear, and in what order |
| The center line, the control limits, and the zone lines | The rules that are switched on, and their thresholds |
| Every sigma estimate and its degrees of freedom | The sigma multiplier |
| The vertical axis, which is now in transformed units | |
| The values reported in the summary table | |
| Any specification limits, target, and the capability results computed from them |
The transformation is fitted once for the whole chart, and it is fitted on the baseline points only, not on all the data. With splits in effect, the single fit uses the union of the per-phase baseline windows, that is exactly the points that feed each phase's own center line and within-phase sigma, and the fitted transformation is then applied to every row of the chart. Individual phases never get their own transformation. Full detail: Splits and Phases.
Blank rows are handled slightly differently by the two transformations while the fit is being made: Box-Cox keeps a blank as a hole, so the moving range chain breaks in exactly the places it would have broken anyway, while the Johnson transformation drops blanks from the values it fits on.
With a transformation active on an Individuals chart, every plotted point is the transformed observation. The vertical axis and every value in the summary table are in transformed units.
Conditional behavior¶
| Condition | Effect |
|---|---|
| Any transformation is active | Manual control limits become unavailable. The Manual option is greyed out, and if it was already selected it reverts to the calculated limits. Limits typed by hand would be in the original units and there is nothing to convert them with. |
| Any transformation is active | The Historical Values boxes are greyed out, and any value already typed there is dropped for this run rather than converted. The typed text stays in the box and takes effect again when the transformation is switched back to None. |
| A transformation is active and a capability analysis is active | Split Control Limits is greyed out entirely and the split mode reverts to None. A capability analysis counts as active as soon as a lower or upper specification limit is entered. This combination can only arise on the charts that offer both a transformation and a Capability tab. |
| A transformation is active and splits are in effect | One transformation for the whole chart, fitted on the union of the per-phase baseline windows, applied to every row. Both the plotted values and the summary table report transformed results. |
| Estimate Limits From is set to a first-N count | The transformation is fitted from that baseline subset, not from all the data. Changing the count changes the transformation, and therefore changes every plotted value. |
| Box-Cox is selected | The Box-Cox transformation is defined for positive values only. Zero and negative measurements cannot be transformed this way. |
Split Control Limits¶
A split divides the chart into consecutive sections, called phases, and gives each phase its own center line and its own control limits. Use it when the process changed on a known date: a new supplier, a tooling change, a settings change. The limits then step at the change instead of averaging across it.
Every phase estimates its own center line, its own sigma, its own control limits, and its own zone lines, and the out-of-control run counters restart at every phase boundary. Splitting never hides or moves a point: all points stay on the chart in their original order, and only the limits they are judged against change. For the formulas, and for the full list of what is shared across the chart versus estimated per phase, see Splits and Phases.
Controls, variable chart dialogs¶
The group box is headed Split Control Limits and holds three mutually exclusive mode buttons plus the editors each mode reveals.
| Label as shown | Control | Default | Valid entries | What it does |
|---|---|---|---|---|
| None | Radio button | Selected | n/a | One center line and one set of limits for the whole chart. |
| Split by column | Radio button | Not selected | n/a | A new phase starts at every row where the chosen column's value changes. |
| (split column list) | Drop-down list, no label of its own | Nothing selected | Any one column offered in the list | Names the column whose value changes drive the phases. |
| Manual break points | Radio button | Not selected | n/a | Phases start at the point numbers you type. |
| (break entry box) | Text box, no label of its own. Tool tip: "Enter a 1-based chart point (subgroup) number" | Empty | A whole number from 1 up to the number of plotted points | Holds one break number until you press Add. It is a staging box; typing in it alone changes nothing. |
| Add | Button | n/a | n/a | Moves the typed number into the break list, in ascending order, and inserts a matching label slot. |
| Remove | Button | n/a | n/a | Deletes the break selected in the list and its label slot. |
| (break list) | List box | Empty | n/a | Shows the break point numbers currently in effect. |
| Split Labels (shown beside each divider): | Label above one text box per phase | One empty box, named "Split 1" | Any text | The text drawn beside each divider on the chart. |
Hidden rather than disabled: the split column list appears only while Split by column is selected, and the break entry box, Add, Remove, the break list, and the whole Split Labels block appear only while Manual break points is selected.
Disabled: the entire group box is greyed out, and the mode reverts to None, when a transformation and a capability analysis are both active. See the conditional behavior table below.
Validation, and what it does not tell you. These dialogs have no validation message line in this group box at all. Add silently refuses the entry, leaving it in the box, when it is not a whole number, when it is below 1, when it is at or beyond the known number of plotted points, or when that break is already in the list. Nothing appears on screen in any of those cases. When the point count is not yet known to the dialog the upper check is skipped, so a break past the end of the data can be added and is dealt with later by the calculation. Remove with nothing selected in the list does nothing and says nothing. There is no check at all on how short a phase the break would create.
What a break number means¶
A break number is the 1-based number of the plotted point that starts the new phase, the same number you read along the horizontal axis, not a worksheet row address. On charts plotted from subgroups it is the subgroup number, not the raw data row. On charts where one row is one point the two are the same.
Breaks must be different from each other and are kept in ascending order for you. A break at point 1 does nothing, because the first phase already starts there.
Split Labels¶
The Split Labels (shown beside each divider): block gives one text box per phase, so the number of boxes is always the number of breaks plus one. Each box is named Split 1, Split 2, and so on, in chart order. Those names are slot names, not the labels: they are fixed and cannot be edited. Whatever you type in the box beside a slot is what gets drawn on the chart. Leaving a box empty draws no label for that phase.
Adding a break inserts a new empty box at the position that changed rather than adding one at the end, so labels already typed stay with the phases they were written for.
The block appears only in the manual break mode. There is no way to type phase labels when the phases come from a column: in column mode the label beside each divider is the split column's own cell value.
The split column is claimed from the Data tab¶
The split column is chosen here, but it is one of the worksheet columns listed on the Data tab, and a column can hold only one job at a time. Choosing a column as the split column claims it: on the Data tab that column is greyed out and can no longer be checked as a measurement column, an X-axis label column, a subgroup ID, or a part column. Releasing it here gives it back. A column already claimed for one of those other jobs appears greyed in the split column list and cannot be picked. Neither the greyed check box on the Data tab nor the greyed list entry here explains which job is holding the column.
Selecting the column mode with no column chosen is not an error. It is a deliberate decision in the product, and it means do not split. Nothing is flagged, no message appears, and the chart is built with one set of limits, exactly as if the mode were None. The same is true of the manual break mode with an empty break list.
Minimum phase length, and two opposite outcomes¶
Every phase has to be long enough to estimate limits from. The minimum differs by chart family, and so does what happens when a break breaks the rule.
| Charts | Shortest phase allowed | A break that would create a shorter phase |
|---|---|---|
| Variable charts | 5 points | The whole analysis is rejected and no chart is produced. |
| Attribute and rare-event charts | 2 points | The break is dropped and the chart is built without it. |
That is the same user action with opposite outcomes: on an attribute chart a too-short phase costs you a divider, on a variable chart it costs you the chart.
The variable chart dialogs validate neither number. They do not check the minimum, and they do not check the arithmetic of the phase lengths your breaks imply, so a set of breaks can be accepted without complaint at entry and then fail when the chart is built. The attribute and rare-event dialogs do check the two-point rule as each break is added, with the message shown above.
A variable chart phase also fails the analysis when it holds fewer than five values that are actually present, even when the phase itself is long enough. Blank rows inside a phase therefore matter as much as its length.
On an Individuals chart the five-point minimum is five observations, and the dialog does not check it, so a break that leaves a phase of four rows is accepted here and then stops the analysis with a message instead of producing a chart.
Conditional behavior¶
| Condition | Effect |
|---|---|
| Any split mode other than None is selected, on a variable chart | Manual control limits become unavailable. The Manual option is greyed out, and if it was already selected it reverts to the calculated limits. |
| A split mode is selected but produces no phases (column mode with no column, or manual mode with an empty list), on a variable chart | Manual control limits are still unavailable. The check looks at which mode button is selected, not at whether any phase boundary results. Setting the mode back to None restores the Manual option. |
| Any split mode selected, on an attribute or rare-event chart | No such restriction. Manual limits stay available, and the band you enter is drawn in every phase. |
| A transformation and a capability analysis are both active | The whole Split Control Limits group box is greyed out and the mode reverts to None. A capability analysis counts as active as soon as a lower or upper specification limit is entered. This can only arise on the charts that offer both a transformation and a Capability tab. |
| A transformation is active, with or without splits | One transformation is fitted for the whole chart and then applied to every row. Phases never get their own transformation. |
| Estimate Limits From, or Baseline Estimation, is set to a first-N count | There is one count for the whole chart. It is reused inside every phase and capped at that phase's length, so a short phase uses all of its own points while a longer phase in the same chart uses the count you typed. There is no per-phase count, and the count never reaches across a phase boundary. See Baseline and Limit Estimation. |
| Out-of-control rules are on | Every run and every window restarts at each phase boundary. A run in progress when a boundary arrives is abandoned, so a run of eight points that straddles a boundary cannot combine into one signal. The point-by-point test against the limits is unaffected, because each point is compared with its own phase's limits. |
| A historical mean or sigma is supplied | The one value you supply is applied to every phase. It is not a per-phase entry. |
Splits are edited after the fact in the Control Chart task pane as well, but only the manual break points and the labels. The column mode cannot be selected or cleared there.
Rules and Display Tab¶
Out-of-Control Rules¶
The group box headed Out-of-Control Rules holds one row per rule. Each row is a check box carrying the rule's description, followed by up to two small numbered boxes labelled N = and M =. N is how many points the rule needs, and M, where a rule has one, is the length of the window those points must fall inside.
Ticking a rule adds its test to the analysis. Nothing else about the chart changes: the center line, the limits, and the plotted points are the same whether a rule is on or off.
Thresholds. Every box arrives pre-filled with that rule's standard value rather than blank, so you can see what the rule will do before you change it. Clearing a box means use the standard value; it does not mean zero. Unticking a rule leaves its numbers visible but locks the boxes, so the value you set is still there when you tick the rule again.
There is no message when a threshold is refused. On the attribute and rare-event dialogs a count below 2 is silently raised to 2 as soon as you leave the box. On the variable chart dialogs a value that is blank, zero, or negative is treated as the standard value.
The rule set on the variable charts¶
Eight rows, and all eight are ticked by default. This is the opposite of the attribute charts, so a chart of the same data can flag very differently depending on which family of chart you chose.
| Row label as shown | Parameters and defaults | Default |
|---|---|---|
| Rule 1 - Beyond K sigma from center | none, see the note below | On |
| Rule 2 - N consecutive points on same side of center | N = 9 | On |
| Rule 3 - N consecutive increasing or decreasing | N = 6 | On |
| Rule 4 - N consecutive alternating up/down | N = 14 | On |
| Rule 5 - N of M beyond 2 sigma (same side) | N = 2, M = 3 | On |
| Rule 6 - N of M beyond 1 sigma (same side) | N = 4, M = 5 | On |
| Rule 7 - N consecutive within 1 sigma | N = 15 | On |
| Rule 8 - N consecutive beyond 1 sigma (either side) | N = 8 | On |
Rule 1 has no parameter box of its own. It tests against the drawn control limits, so its width is the sigma multiplier from the Control Limits section.
What each rule actually tests, and which points of a run get marked, is defined on Out-of-Control Rules.
The Individuals variant shows all eight rows, and all eight are on when the dialog opens.
Which panels the rules run on¶
Every panel is checked, the dispersion panels included. On a two-panel or three-panel chart the range, standard deviation, and moving range panels each run their rules over their own plotted values, against their own center line and their own limits.
Rules 5 through 8 are the exception. They read the zone lines and assume a symmetric spread around the center line, which a range or a standard deviation does not have, so they run on the location panel only.
| Panel | Rules that run there |
|---|---|
| Xbar, Individuals, or EWMA (the location panel) | Every rule the chart offers |
| Range, standard deviation, moving range | 1, 2, 3, 4 |
| Z-MR moving range panel | 1, 2, 3 |
| Single-panel charts | Every rule the chart offers |
What the group box does about it depends on which panels the chart is drawing:
- On a variant that draws a dispersion panel only, such as R only, S only, or Moving Range only, the rows for rules 5 through 8 are greyed out along with their threshold boxes. Greying them does not clear them: whatever you had ticked is still ticked if you switch the panel view back.
- On a chart that draws the location panel next to a companion panel, those rows stay available and an italic note appears under the list reading "Rules 5-8 only apply to" followed by the name of the location panel.
This variant draws the location panel and nothing else, so all eight rules run on it and every row stays available. There is no companion panel to restrict rules 5 through 8, and the dialog shows no note about them, unlike the I-MR variant where the note names the Individuals panel.
The sigma multiplier is also a rule setting
Rule 1 tests each point against the drawn control limits, so editing the number of standard deviations in the Control Limits section changes the Rule 1 test at the same time as it changes the limits. That is why Rule 1 has no threshold box of its own. On the variable charts it also moves the zone lines, and therefore changes what rules 5 through 8 test.
Conditional behavior¶
| Condition | Effect |
|---|---|
| Control limits set to None, on a variable chart | No rule fires. Every rule result is cleared along with the limits, so no point is marked even though the rules are still ticked. |
| Control limits set to None, on an attribute or rare-event chart | The center line is still estimated, so rules 2, 3, and 4, and Rule 9 on a G chart, still fire and still mark points. Rule 1 cannot fire, because there are no limits to exceed. |
| Control limits set to Manual | The rules run against the band you entered, and the zone lines are derived from that band. |
| Manual limits entered with the center left blank, on an attribute chart | There is no center line and no zone lines, so rules 2, 3, and 4 cannot fire. |
| Splits are in effect | Every run and every window restarts at each phase boundary. A run in progress when a boundary arrives is abandoned and cannot combine with the run that starts after it. |
| A point is blank or excluded | Runs break at the gap rather than bridging it. For the two window rules, rules 5 and 6, a blank invalidates every window that overlaps it, not just the run. |
| A rule is unticked | Its threshold value is kept and its box is locked. Nothing is lost by turning a rule off and on again. |
| The sigma multiplier is changed, on a variable chart | The zone lines move with the band, because they are placed at thirds of it. At a multiplier other than 3 the line labelled 2 sigma is not at 2 sigma, which changes what rules 5 through 8 test. On the attribute charts and Z-MR the zone lines are at a true 1 and 2 sigma at any multiplier. |
| A capability analysis or a transformation is active | Neither affects the rules. The rule set, the thresholds, and the panels checked are the same. |
Background reading for your operators: Out-of-Control tests.
The chart does not tell you which rule fired
Every rule you tick is tested, and the results are combined into a single verdict per point: this point broke at least one enabled rule, or it did not. Points that broke one are drawn in a different color from the rest, and that is the whole of the report. There is no per-rule label, no per-rule marker, no per-rule column, and no list of violations anywhere in the chart or the worksheet. A point that breaks four rules at once looks exactly like a point that breaks one, and the output never names either.
So when you turn several rules on, read a marked point as an instruction to go and look at the chart, not as a diagnosis. If you need to know which pattern caused a particular signal, the practical method is to switch the other rules off and rebuild the chart.
Display Options¶
The Display Options group box holds two features: the sigma zone lines, and reference lines of your own at Y values you choose. It is the same group box on every control chart. The variable charts take it from a shared control, and the p, np, Laney P', c, u, Laney U', G, and T dialogs repeat the same block with the same labels.
- Show 1-sigma / 2-sigma zone lines: draws four light grey lines inside the control band, two above the center line and two below, dividing each side into three zones. The checkbox is cleared by default.
The zone lines are always built into the chart. This checkbox only decides whether they start out visible, so they can be shown or hidden later from the Analysis Pane without running the analysis again.
Where the lines are placed is not the same on every chart, and on a variable chart drawn with a sigma multiplier other than 3 the names 1-sigma and 2-sigma do not describe where the lines actually sit. Since several of the out-of-control tests measure a point against these zones, this changes what those tests count. The placement rule for each chart family is on Control Limits and Zones.
The two dialog families treat the checkbox differently when Control limits is set to None. On the variable charts the checkbox stays available, but with no control band there is nothing to divide into zones and no lines are drawn. On the attribute and rare event charts the checkbox is disabled and cleared for you.
Reference lines¶
A reference line is a horizontal line at a Y value you supply: a specification limit, a target, a contract threshold, anything you want the points compared against. Until you add one the editor reads "No reference lines configured. Use the row editor below to add Y-value reference lines."
Each reference line is one row with four editable cells and a remove button:
| Cell | What it sets | Default |
|---|---|---|
| Value | the Y position of the line | 0 |
| Label | the legend entry for the line | blank |
| Color | the line color, picked from a color button | red |
| Thickness | the line weight, chosen from 0.5, 1.0, 1.5, and 2.0 | 1.0 |
| X | removes that row. Its tooltip reads "Remove this reference line" | n/a |
Value is not validated. Type something that is not a number and the cell keeps the value it had. A blank Label keeps the line out of the chart legend; the line is still drawn, under a generated name built from its value. The editor scrolls on its own once the list of rows is taller than the space allowed for it.
- Add Reference Line: appends a blank row and refreshes the chart preview by itself. Removing a row with its X button does the same.
- Apply: commits edits to Value, Label, Color, and Thickness, which do not refresh the preview on their own. Its tooltip reads "Refresh the chart preview to reflect any pending reference-line edits". The button appears only once at least one reference line exists, and does nothing when there is nothing outstanding to commit.
So adding and removing lines is immediate, while editing an existing line needs Apply.
Reference lines are drawn on the location panel only
Reference lines appear on the panel that plots the measurement itself: the Xbar panel, the Individuals panel, the EWMA panel, or the Z panel of a Z-MR chart. The dispersion panels (Range, Standard Deviation, Moving Range) are in different units, so they never carry reference lines. The location panel's Y axis is stretched to include every reference line value, so a line outside the data still shows.
This has a consequence on the single-panel dispersion charts. R only, S only, and Moving Range only draw no location panel, so a reference line entered in the editor never appears anywhere on the chart. The editor still accepts it and still lists it. If you need a reference line against a range or a standard deviation, there is no dialog option that will draw one.
CUSUM is the exception: it is a single overlay chart rather than stacked panels, and it draws reference lines on that chart.
The Individuals panel is the location panel, and on this variant it is the only panel, so every reference line you add is drawn.
Layout you do not choose¶
Nothing else about the appearance of the chart is a dialog option. These are fixed:
- Which panels are drawn comes from the ribbon entry you started from, not from a checkbox in the dialog. Choosing R rather than Xbar-R is how you get the range panel on its own.
- Panel titles are composed for you from the panel type, the group, and the measurement column name, with empty parts dropped.
- Plot order is fixed, and it is also the front-to-back order: the data line, then the zone lines, then the upper and lower control limits, then the center line, then the reference lines. The zone lines are added before the limits deliberately, so they stay in the background.
- Axes are set for you. The X axis is numbered by plotted point and titled Subgroup. The Y axis is scaled to fit every plotted value, including the zone lines and, on the location panel, the reference lines; dispersion panels are held at or above zero. When a chart has more than one panel the panels are aligned with each other so their points line up vertically.
Once the chart exists, the zone lines can be shown or hidden from the Analysis Pane without running anything again. Reference lines cannot: they are not in the pane, so to add, edit, or remove one you modify the analysis and run it again.
Capability Tab¶
The Capability tab attaches a capability analysis to the chart. It holds five groups: Specification Limits (LSL:, Target:, and USL:), Process Capability Standard, the capability Confidence Intervals, Goodness of Fit, and the histogram bin settings.
Nothing on this tab produces output until you enter a specification limit or a target. With all three boxes empty the settings are still stored, but no capability block and no histogram are written to the worksheet, no capability index is reported, and the goodness-of-fit test does not run even though a method is selected.
Two interactions belong to this tab rather than to the capability settings themselves:
- Entering a specification limit switches First N subgroups off. Type a value in LSL: or USL: and, on the Limits and Estimation tab, the First N subgroups: radio greys out and the selection returns to All subgroups, with no message. Clearing the specification limit makes it available again. A Target: on its own does not grey it out, but do not read that as permission: a target alone still switches the capability calculation on, and the engine refuses to combine capability with a First N baseline, so running that combination produces no chart and the message "Capability cannot be combined with a First-N baseline."
- A specification limit together with a transformation switches splits off. The whole Split Control Limits group greys out and the split mode returns to None.
As on every control chart, a control chart never fits a distribution other than the normal. There is no fit-type choice on this tab and no distribution comparison table in the output. If your measurements are badly skewed, the remedy on a chart is the Transformation group on the Limits and Estimation tab.
Every one of these groups is the same control as in the Capability Analysis tool, and the settings are described in one place, on the Capability Analysis and Histogram Options page.
Task Pane¶
The Control Chart pane is the same on every chart and is described on Create Control Charts. On an Individuals sheet it binds to the worksheet named Individuals Chart.
Apply Splits is rejected when the chart was built with manual limits, or with a transformation and a specification limit together. Both are the combinations the dialog already refuses to split.